Method and apparatus for intra prediction

ABSTRACT

Apparatuses and methods for intra predicting a block are described. The method of intra predicting a current block can include obtaining a predicted sample value from one or more reference sample values by using an intra prediction mode, obtaining at least one additional reference sample value in accordance with the intra prediction mode, and obtaining a thresholded additional reference sample value based on the additional reference sample value. The method can also include calculating an additional value from the thresholded additional reference sample value, multiplying the predicted sample value by a sample weighting factor, resulting in a weighted predicted sample value, adding the additional value to the weighted predicted sample value, resulting in a non-normalized predicted sample value, and normalizing the non-normalized predicted sample value, resulting in a normalized predicted sample values. The accuracy for the intra prediction is thus increased.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/RU2019/050262, filed on Dec. 30, 2019, which claims the benefit ofU.S. Provisional Application No. 62/786,349, filed on Dec. 29, 2018 andU.S. Provisional Application No. 62/821,422, filed on Mar. 20, 2019. Allof the aforementioned patent applications are hereby incorporated byreference in their entireties.

TECHNICAL FIELD

The present disclosure relates to the technical field of image and/orvideo coding and decoding, and in particular to method and apparatus forintra prediction.

BACKGROUND

Digital video has been widely used since the introduction of DVD-discs.Before transmission the video is encoded and transmitted using atransmission medium. The viewer receives the video and uses a viewingdevice to decode and display the video. Over the years the quality ofvideo has improved, for example, because of higher resolutions, colordepths and frame rates. This has lead into larger data streams that arenowadays commonly transported over internet and mobile communicationnetworks.

Higher resolution videos, however, typically require more bandwidth asthey have more information. In order to reduce bandwidth requirementsvideo coding standards involving compression of the video have beenintroduced. When the video is encoded the bandwidth requirements (orcorresponding memory requirements in case of storage) are reduced. Oftenthis reduction comes at the cost of quality. Thus, the video codingstandards try to find a balance between bandwidth requirements andquality.

The High Efficiency Video Coding (HEVC) is an example of a video codingstandard that is commonly known to persons skilled in the art. In HEVC,a coding unit (CU) is split into prediction units (PU) or transformunits (TUs). The Versatile Video Coding (VVC) next generation standardis the most recent joint video project of the ITU-T Video Coding ExpertsGroup (VCEG) and the ISO/IEC Moving Picture Experts Group (MPEG)standardization organizations, working together in a partnership knownas the Joint Video Exploration Team (WET). VVC is also referred to asITU-T H.266/Next Generation Video Coding (NGVC) standard. In VVC, theconcepts of multiple partition types shall be removed, i.e. theseparation of the CU, PU and TU concepts except as needed for CUs thathave a size too large for the maximum transform length, and supportsmore flexibility for CU partition shapes.

Processing of these coding units (CUs) (also referred to as blocks)depends on their size, spatial position and a coding mode specified byan encoder. Coding modes can be classified into two groups according tothe type of prediction: intra-prediction and inter-prediction modes.Intra prediction modes use samples of the same picture (also referred toas frame or image) to generate reference samples to calculate theprediction values for the samples of the block being reconstructed.Intra prediction is also referred to as spatial prediction.Inter-prediction modes are designed for temporal prediction and usesreference samples of previous or next pictures to predict samples of theblock of the current picture.

There is a need for apparatuses and methods for video coding, whichallow for an efficient handling of an intra prediction process.

SUMMARY

Methods of intra predicting a block of a picture, encoding device,decoding device, and computer-readable medium are provided.

As an example of a first aspect of the invention, a method of intrapredicting a block of a picture is provided, and the method includes:

obtaining a predicted sample value from one or more reference samplevalues by intra-prediction using an intra predication mode, wherein theintra prediction mode is one of a DC intra prediction mode, a horizontalintra-predication mode, or a vertical intra predication mode;

obtaining the values of the nearest reference samples located above andto the left of the predicted sample;

obtaining, in accordance with the intra prediction mode, one or moreadditional reference sample values, wherein:

-   -   when the intra prediction mode is vertical, additional reference        sample value is set equal to the difference between the value of        the nearest reference sample located above the predicted sample        and the value of the top-left reference sample,    -   when the intra prediction mode is horizontal, additional        reference sample value is set equal to the difference between        the value of the nearest reference sample located to the left of        the predicted sample and the value of the top-left reference        sample,    -   when the intra prediction mode is a DC intra prediction mode,        the first additional reference sample value and the second        additional reference sample value are obtained by        -   etting the first additional reference sample value equal to            the value of the nearest reference sample located to the            left of the predicted sample, and        -   etting the second additional reference sample value equal to            the value of the nearest reference sample located above the            predicted sample;    -   thresholding an additional reference sample value when the intra        prediction mode is either horizontal or vertical;    -   calculating an additional value either        -   s a weighted sum of the first additional reference sample            and the second additional reference sample when the intra            prediction mode is a DC intra prediction mode, or        -   y multiplying weighting factor by the additional reference            sample value when the intra prediction mode is either            horizontal or vertical;

multiplying the predicted sample value by a sample weighting factor,resulting in a weighted predicted sample value, wherein the sampleweighting factor is set equal to one when the intra prediction mode iseither horizontal or vertical;

adding an additional value to the weighted predicted sample value,resulting in a non-normalized predicted sample value; and

normalizing the non-normalized predicted sample value by an arithmeticright shift of an integer representation of the non-normalized predictedsample value, resulting in a normalized predicted sample value.

As an embodiment of the first aspect, the method further includesderivation of the minimum and maximum values of a predicted sample,where thresholding an additional reference sample value includes:

obtaining top-left reference sample value; and

updating the additional reference sample value, comprising a checkwhether it is greater than an upper limit value or lower than a lowerlimit, wherein

-   -   when the top-left reference sample value is greater than the        predicted sample value, the upper limit is obtained by        subtracting predicted sample value from the maximum value of the        predicted sample, the updated additional reference sample value        is set equal to the maximum of two values,        -   the first value is the additional reference sample value,            and        -   the second value is the upper limit,    -   otherwise, the lower limit is obtained by subtracting predicted        sample value from the minimum value of the predicted sample, the        updated additional reference sample value is set equal to the        minimum of two values,        -   the first value is the additional reference sample value,            and        -   the second value is the lower limit.

As an example of a second aspect of an embodiment of the invention, amethod of intra predicting a block of a picture is provided, and themethod includes: obtaining an intra prediction mode of a current block;and performing position-dependent prediction combination (PDPC) based onthe top sample or left sample when the intra prediction mode is DC modeor planar mode, top-left sample is not used for position-dependentprediction combination (PDPC).

As an example of a third aspect of an embodiment of the invention, amethod of intra predicting a block of a picture is provided, and themethod includes: obtaining an intra prediction mode of a current block;clipping operation in position-dependent prediction combination (PDPC)is performed when the intra prediction mode is horizontal intraprediction mode or vertical intra prediction mode, and is not performedwhen the intra prediction mode is DC mode or planar mode.

As an embodiment of the third aspect, the clipping operation in PDPC isperformed only when the intra prediction mode is the horizontal intraprediction mode or the vertical intra prediction mode. For example, whenpredModeIntra is equal to INTRA_ANGULAR18 or INTRA_ANGULAR50:

predSamples[x][y]=clip1Cmp((refL[x][y]*wL[x]+refT[x][y]*wT[y]−p[−1][−1]*wTL[x][y]+(64−wL[x]−wT[y]+wTL[x][y])*predSamples[x][y]+32)>>6);

wherein predModeIntra is used to indicate the intra prediction mode,{x,y} define position of a predicted sample, wT, wL and wTL are weightsassociated with reference samples in accordance with the definedposition.

The method according to the first aspect or any possible embodiment ofthe first aspect, the second aspect or any possible embodiment of thesecond aspect, or the third aspect or any possible embodiment of thethird aspect, can be performed by the apparatus according to the fourthaspect of the invention.

According to a fifth aspect, embodiments of the invention relate to anapparatus for decoding a video stream includes a processor and a memory.The memory is storing instructions that cause the processor to performthe method according to the first aspect or any possible embodiment ofthe first aspect, the second aspect or any possible embodiment of thesecond aspect, or the third aspect or any possible embodiment of thethird aspect.

According to a sixth aspect, embodiments of the invention relate to anapparatus for encoding a video stream includes a processor and a memory.The memory is storing instructions that cause the processor to performthe method according to the first aspect or any possible embodiment ofthe first aspect, the second aspect or any possible embodiment of thesecond aspect, or the third aspect or any possible embodiment of thethird aspect.

According to a seventh aspect, a computer-readable storage medium havingstored thereon instructions that when executed cause one or moreprocessors configured to code video data is proposed. The instructionscause the one or more processors to perform a method according to thefirst aspect or any possible embodiment of the first aspect, the secondaspect or any possible embodiment of the second aspect, or the thirdaspect or any possible embodiment of the third aspect.

According to an eighth aspect, embodiments of the invention relate to acomputer program comprising program code for performing the methodaccording to the first aspect or any possible embodiment of the firstaspect, the second aspect or any possible embodiment of the secondaspect, or the third aspect or any possible embodiment of the thirdaspect when executed on a computer.

Details of one or more embodiments are set forth in the accompanyingdrawings and in the description below. Other features, objects, andadvantages will be apparent from the description, drawings, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following embodiments of the invention are described in moredetail with reference to the attached figures and drawings, in which:

FIG. 1A is a block diagram showing an example of a video coding systemconfigured to implement embodiments of the invention;

FIG. 1B is a block diagram showing another example of a video codingsystem configured to implement embodiments of the invention;

FIG. 2 is a block diagram showing an example of a video encoderconfigured to implement embodiments of the invention;

FIG. 3 is a block diagram showing an example structure of a videodecoder configured to implement embodiments of the invention;

FIG. 4 is a block diagram illustrating an example of an encodingapparatus or a decoding apparatus;

FIG. 5 is a block diagram illustrating another example of an encodingapparatus or a decoding apparatus;

FIG. 6 illustrates an example of Angular intra prediction directions andmodes and the associated value of p_(ang) for vertical predictiondirections;

FIG. 7 illustrates an example of Transformation of p_(ref) to p_(1, ref)for a 4×4 block;

FIG. 8 illustrates an example of Construction of p_(1,ref) forhorizontal angular prediction;

FIG. 9 illustrates an example of Construction of p_(1,ref) for verticalangular prediction;

FIG. 10A illustrates an example of Angular intra prediction directionsand the associated intra-prediction modes in JEM and BMS-1;

FIG. 10B illustrates an example of Angular intra prediction directionsand the associated intra-prediction modes in VTM-2;

FIG. 10C illustrates an example of Angular intra prediction directionsand the associated intra-prediction modes in VTM-3;

FIG. 11 illustrates an example of Angular intra prediction directionsand the associated intra-prediction modes in HEVC;

FIG. 12 illustrates an example of QTBT explained;

FIG. 13A illustrates an example of coordinates for vertical andhorizontal intra prediction modes;

FIG. 13B illustrates an example of DC mode PDPC weights for (0, 0) and(1, 0) positions inside a 4×4 block;

FIG. 14 illustrates an example of intra-predicting a block fromreference samples of the main reference side;

FIG. 15 illustrates an example of DC mode PDPC weights for (0, 0) and(1, 0) positions inside a 4×4 block;

FIG. 16 illustrates an example of intra-predicting a block of samples;

FIG. 17 illustrates an example that reference samples are used by theintra prediction process to produce predicted samples;

FIG. 18 is a block diagram showing an example structure of an apparatusfor intra prediction to produce predicted samples;

FIG. 19 is a block diagram showing an example structure of a contentsupply system 3100 which realizes a content delivery service; and

FIG. 20 is a block diagram showing a structure of an example of aterminal device.

In the following identical reference signs refer to identical or atleast functionally equivalent features if not explicitly specifiedotherwise.

DETAILED DESCRIPTION OF THE EMBODIMENTS Definitions of Acronyms &Glossary

JEM - Joint Exploration Model (the software codebase for future videocoding exploration) JVET - Joint Video Experts Team LUT - Look-Up TablePDPC - Position-dependent prediction combination PPS - Picture parameterset QT - QuadTree QTBT - QuadTree plus Binary Tree RDO - Rate-distortionOptimization ROM - Read-Only Memory SPS - Sequence parameter set VTM -VVC Test Model VVC - Versatile Video Coding, the standardization projectdeveloped by JVET. CTU/CTB - Coding Tree Unit/Coding Tree Block CU/CB -Coding Unit/Coding Block PU/PB - Prediction Unit/Prediction BlockTU/TB - Transform Unit/Transform Block HEVC - High Efficiency VideoCoding

In the following description, reference is made to the accompanyingfigures, which form part of the disclosure, and which show, by way ofillustration, specific aspects of embodiments of the invention orspecific aspects in which embodiments of the present invention may beused. It is understood that embodiments of the invention may be used inother aspects and comprise structural or logical changes not depicted inthe figures. The following detailed description, therefore, is not to betaken in a limiting sense, and the scope of the present invention isdefined by the appended claims.

For instance, it is understood that a disclosure in connection with adescribed method may also hold true for a corresponding device or systemconfigured to perform the method and vice versa. For example, if one ora plurality of specific method steps are described, a correspondingdevice may include one or a plurality of units, e.g., functional units,to perform the described one or plurality of method steps (e.g., oneunit performing the one or plurality of steps, or a plurality of unitseach performing one or more of the plurality of steps), even if such oneor more units are not explicitly described or illustrated in thefigures. On the other hand, for example, if a specific apparatus isdescribed based on one or a plurality of units, e.g., functional units,a corresponding method may include one step to perform the functionalityof the one or plurality of units (e.g., one step performing thefunctionality of the one or plurality of units, or a plurality of stepseach performing the functionality of one or more of the plurality ofunits), even if such one or plurality of steps are not explicitlydescribed or illustrated in the figures. Further, it is understood thatthe features of the various exemplary embodiments and/or aspectsdescribed herein may be combined with each other, unless specificallynoted otherwise.

Video coding typically refers to the processing of a sequence ofpictures, which form the video or video sequence. Instead of the term“picture” the term “frame” or “image” may be used as synonyms in thefield of video coding. Video coding (or coding in general) comprises twoparts, i.e. video encoding and video decoding. Video encoding isperformed at the source side, typically comprising processing (e.g., bycompression) the original video pictures to reduce the amount of datarequired for representing the video pictures (for more efficient storageand/or transmission). Video decoding is performed at the destinationside and typically comprises the inverse processing compared to theencoder to reconstruct the video pictures. Embodiments referring to“coding” of video pictures (or pictures in general) shall be understoodto relate to “encoding” or “decoding” of video pictures or respectivevideo sequences. The combination of the encoding part and the decodingpart is also referred to as CODEC (Coding and Decoding).

In case of lossless video coding, the original video pictures can bereconstructed, i.e. the reconstructed video pictures have the samequality as the original video pictures (assuming no transmission loss orother data loss during storage or transmission). In case of lossy videocoding, further compression, e.g., by quantization, is performed, toreduce the amount of data representing the video pictures, which cannotbe completely reconstructed at the decoder, i.e. the quality of thereconstructed video pictures is lower or worse compared to the qualityof the original video pictures.

Several video coding standards belong to the group of “lossy hybridvideo codecs” (i.e. combine spatial and temporal prediction in thesample domain and 2D transform coding for applying quantization in thetransform domain). Each picture of a video sequence is typicallypartitioned into a set of non-overlapping blocks and the coding istypically performed on a block level. In other words, at the encoder thevideo is typically processed, i.e. encoded, on a block (video block)level, e.g., by using spatial (intra picture) prediction and/or temporal(inter picture) prediction to generate a prediction block, subtractingthe prediction block from the current block (block currentlyprocessed/to be processed) to obtain a residual block, transforming theresidual block and quantizing the residual block in the transform domainto reduce the amount of data to be transmitted (compression), whereas atthe decoder the inverse processing compared to the encoder is applied tothe encoded or compressed block to reconstruct the current block forrepresentation. Furthermore, the encoder duplicates the decoderprocessing loop such that both will generate identical predictions(e.g., intra- and inter predictions) and/or re-constructions forprocessing, i.e. coding, the subsequent blocks.

In the following embodiments of a video coding system 10, a videoencoder 20 and a video decoder 30 are described based on FIGS. 1 to 3.

FIG. 1A is a schematic block diagram illustrating an example codingsystem 10, e.g., a video coding system 10 (or short coding system 10)that may utilize techniques of this present application. Video encoder20 (or short encoder 20) and video decoder 30 (or short decoder 30) ofvideo coding system 10 represent examples of devices that may beconfigured to perform techniques in accordance with various examplesdescribed in the present application.

As shown in FIG. 1A, the coding system 10 comprises a source device 12configured to provide encoded picture data 21 e.g., to a destinationdevice 14 for decoding the encoded picture data 21.

The source device 12 comprises an encoder 20, and may additionally, i.e.optionally, comprise a picture source 16, a pre-processor (orpre-processing unit) 18, e.g., a picture pre-processor 18, and acommunication interface or communication unit 22.

The picture source 16 may comprise or be any kind of picture capturingdevice, for example a camera for capturing a real-world picture, and/orany kind of a picture generating device, for example a computer-graphicsprocessor for generating a computer animated picture, or any kind ofother device for obtaining and/or providing a real-world picture, acomputer generated picture (e.g., a screen content, a virtual reality(VR) picture) and/or any combination thereof (e.g., an augmented reality(AR) picture). The picture source may be any kind of memory or storagestoring any of the aforementioned pictures.

In distinction to the pre-processor 18 and the processing performed bythe pre-processing unit 18, the picture or picture data 17 may also bereferred to as raw picture or raw picture data 17.

Pre-processor 18 is configured to receive the (raw) picture data 17 andto perform pre-processing on the picture data 17 to obtain apre-processed picture 19 or pre-processed picture data 19.Pre-processing performed by the pre-processor 18 may, e.g., comprisetrimming, color format conversion (e.g., from RGB to YCbCr), colorcorrection, or de-noising. It can be understood that the pre-processingunit 18 may be optional component.

The video encoder 20 is configured to receive the pre-processed picturedata 19 and provide encoded picture data 21 (further details will bedescribed below, e.g., based on FIG. 2).

Communication interface 22 of the source device 12 may be configured toreceive the encoded picture data 21 and to transmit the encoded picturedata 21 (or any further processed version thereof) over communicationchannel 13 to another device, e.g., the destination device 14 or anyother device, for storage or direct reconstruction.

The destination device 14 comprises a decoder 30 (e.g., a video decoder30), and may additionally, i.e. optionally, comprise a communicationinterface or communication unit 28, a post-processor 32 (orpost-processing unit 32) and a display device 34.

The communication interface 28 of the destination device 14 isconfigured receive the encoded picture data 21 (or any further processedversion thereof), e.g., directly from the source device 12 or from anyother source, e.g., a storage device, e.g., an encoded picture datastorage device, and provide the encoded picture data 21 to the decoder30.

The communication interface 22 and the communication interface 28 may beconfigured to transmit or receive the encoded picture data 21 or encodeddata 13 via a direct communication link between the source device 12 andthe destination device 14, e.g., a direct wired or wireless connection,or via any kind of network, e.g., a wired or wireless network or anycombination thereof, or any kind of private and public network, or anykind of combination thereof.

The communication interface 22 may be, e.g., configured to package theencoded picture data 21 into an appropriate format, e.g., packets,and/or process the encoded picture data using any kind of transmissionencoding or processing for transmission over a communication link orcommunication network.

The communication interface 28, forming the counterpart of thecommunication interface 22, may be, e.g., configured to receive thetransmitted data and process the transmission data using any kind ofcorresponding transmission decoding or processing and/or de-packaging toobtain the encoded picture data 21.

Both, communication interface 22 and communication interface 28 may beconfigured as unidirectional communication interfaces as indicated bythe arrow for the communication channel 13 in FIG. 1A pointing from thesource device 12 to the destination device 14, or bi-directionalcommunication interfaces, and may be configured, e.g., to send andreceive messages, e.g., to set up a connection, to acknowledge andexchange any other information related to the communication link and/ordata transmission, e.g., encoded picture data transmission.

The decoder 30 is configured to receive the encoded picture data 21 andprovide decoded picture data 31 or a decoded picture 31 (further detailswill be described below, e.g., based on FIG. 3 or FIG. 5).

The post-processor 32 of destination device 14 is configured topost-process the decoded picture data 31 (also called reconstructedpicture data), e.g., the decoded picture 31, to obtain post-processedpicture data 33, e.g., a post-processed picture 33. The post-processingperformed by the post-processing unit 32 may comprise, e.g., colorformat conversion (e.g., from YCbCr to RGB), color correction, trimming,or re-sampling, or any other processing, e.g., for preparing the decodedpicture data 31 for display, e.g., by display device 34.

The display device 34 of the destination device 14 is configured toreceive the post-processed picture data 33 for displaying the picture,e.g., to a user or viewer. The display device 34 may be or comprise anykind of display for representing the reconstructed picture, e.g., anintegrated or external display or monitor. The displays may, e.g.,comprise liquid crystal displays (LCD), organic light emitting diodes(OLED) displays, plasma displays, projectors, micro LED displays, liquidcrystal on silicon (LCoS), digital light processor (DLP) or any kind ofother display.

Although FIG. 1A depicts the source device 12 and the destination device14 as separate devices, embodiments of devices may also comprise both orboth functionalities, the source device 12 or correspondingfunctionality and the destination device 14 or correspondingfunctionality. In such embodiments the source device 12 or correspondingfunctionality and the destination device 14 or correspondingfunctionality may be implemented using the same hardware and/or softwareor by separate hardware and/or software or any combination thereof.

As will be apparent for the skilled person based on the description, theexistence and (exact) split of functionalities of the different units orfunctionalities within the source device 12 and/or destination device 14as shown in FIG. 1A may vary depending on the actual device andapplication.

The encoder 20 (e.g., a video encoder 20) and the decoder 30 (e.g., avideo decoder 30) each may be implemented as any of a variety ofsuitable circuitry as shown in FIG. 1B, such as one or moremicroprocessors, digital signal processors (DSPs), application-specificintegrated circuits (ASICs), field-programmable gate arrays (FPGAs),discrete logic, hardware, or any combinations thereof. If the techniquesare implemented partially in software, a device may store instructionsfor the software in a suitable, non-transitory computer-readable storagemedium and may execute the instructions in hardware using one or moreprocessors to perform the techniques of this disclosure. Any of theforegoing (including hardware, software, a combination of hardware andsoftware, etc.) may be considered to be one or more processors. Each ofvideo encoder 20 and video decoder 30 may be included in one or moreencoders or decoders, either of which may be integrated as part of acombined encoder/decoder (CODEC) in a respective device.

Source device 12 and destination device 14 may comprise any of a widerange of devices, including any kind of handheld or stationary devices,e.g., notebook or laptop computers, mobile phones, smart phones, tabletsor tablet computers, cameras, desktop computers, set-top boxes,televisions, display devices, digital media players, video gamingconsoles, video streaming devices (such as content services servers orcontent delivery servers), broadcast receiver device, broadcasttransmitter device, or the like and may use no or any kind of operatingsystem. In some cases, the source device 12 and the destination device14 may be equipped for wireless communication. Thus, the source device12 and the destination device 14 may be wireless communication devices.

In some cases, video coding system 10 illustrated in FIG. 1A is merelyan example and the techniques of the present application may apply tovideo coding settings (e.g., video encoding or video decoding) that donot necessarily include any data communication between the encoding anddecoding devices. In other examples, data is retrieved from a localmemory, streamed over a network, or the like. A video encoding devicemay encode and store data to memory, and/or a video decoding device mayretrieve and decode data from memory. In some examples, the encoding anddecoding is performed by devices that do not communicate with oneanother, but simply encode data to memory and/or retrieve and decodedata from memory.

FIG. 1B is an illustrative diagram of another example video codingsystem 40 including encoder 20 of FIG. 2 and/or decoder 30 of FIG. 3according to an exemplary embodiment. The system 40 can implementtechniques in accordance with various examples described in the presentapplication. In the illustrated implementation, video coding system 40may include imaging device(s) 41, video encoder 100, video decoder 30(and/or a video coder implemented via logic circuitry 47 of processingunit(s) 46), an antenna 42, one or more processor(s) 43, one or morememory store(s) 44, and/or a display device 45.

As illustrated, imaging device(s) 41, antenna 42, processing unit(s) 46,logic circuitry 47, video encoder 20, video decoder 30, processor(s) 43,memory store(s) 44, and/or display device 45 may be capable ofcommunication with one another. As discussed, although illustrated withboth video encoder 20 and video decoder 30, video coding system 40 mayinclude only video encoder 20 or only video decoder 30 in variousexamples.

As shown, in some examples, video coding system 40 may include antenna42. Antenna 42 may be configured to transmit or receive an encodedbitstream of video data, for example. Further, in some examples, videocoding system 40 may include display device 45. Display device 45 may beconfigured to present video data. As shown, in some examples, logiccircuitry 47 may be implemented via processing unit(s) 46. Processingunit(s) 46 may include application-specific integrated circuit (ASIC)logic, graphics processor(s), general purpose processor(s), or the like.Video coding system 40 also may include optional processor(s) 43, whichmay similarly include application-specific integrated circuit (ASIC)logic, graphics processor(s), general purpose processor(s), or the like.In some examples, logic circuitry 47 may be implemented via hardware,video coding dedicated hardware, or the like, and processor(s) 43 mayimplemented general purpose software, operating systems, or the like. Inaddition, memory store(s) 44 may be any type of memory such as volatilememory (e.g., Static Random Access Memory (SRAM), Dynamic Random AccessMemory (DRAM), etc.) or non-volatile memory (e.g., flash memory, etc.),and so forth. In a non-limiting example, memory store(s) 44 may beimplemented by cache memory. In some examples, logic circuitry 47 mayaccess memory store(s) 44 (for implementation of an image buffer forexample). In other examples, logic circuitry 47 and/or processingunit(s) 46 may include memory stores (e.g., cache or the like) for theimplementation of an image buffer or the like.

In some examples, video encoder 20 implemented via logic circuitry mayinclude an image buffer (e.g., via either processing unit(s) 46 ormemory store(s) 44)) and a graphics processing unit (e.g., viaprocessing unit(s) 46). The graphics processing unit may becommunicatively coupled to the image buffer. The graphics processingunit may include video encoder 20 as implemented via logic circuitry 47to embody the various modules as discussed with respect to FIG. 2 and/orany other encoder system or subsystem described herein. The logiccircuitry may be configured to perform the various operations asdiscussed herein.

Video decoder 30 may be implemented in a similar manner as implementedvia logic circuitry 47 to embody the various modules as discussed withrespect to decoder 30 of FIG. 3 and/or any other decoder system orsubsystem described herein. In some examples, video decoder 30implemented via logic circuitry may include an image buffer (e.g., viaeither processing unit(s) 46 or memory store(s) 44)) and a graphicsprocessing unit (e.g., via processing unit(s) 46). The graphicsprocessing unit may be communicatively coupled to the image buffer. Thegraphics processing unit may include video decoder 30 as implemented vialogic circuitry 47 to embody the various modules as discussed withrespect to FIG. 3 and/or any other decoder system or subsystem describedherein.

In some examples, antenna 42 of video coding system 40 may be configuredto receive an encoded bitstream of video data. As discussed, the encodedbitstream may include data, indicators, index values, mode selectiondata, or the like associated with encoding a video frame as discussedherein, such as data associated with the coding partition (e.g.,transform coefficients or quantized transform coefficients, optionalindicators (as discussed), and/or data defining the coding partition).Video coding system 40 may also include video decoder 30 coupled toantenna 42 and configured to decode the encoded bitstream. The displaydevice 45 configured to present video frames.

For convenience of description, embodiments of the invention aredescribed herein, for example, by reference to High-Efficiency VideoCoding (HEVC) or to the reference software of Versatile Video coding(VVC), the next generation video coding standard developed by the JointCollaboration Team on Video Coding (JCT-VC) of ITU-T Video CodingExperts Group (VCEG) and ISO/IEC Motion Picture Experts Group (MPEG).One of ordinary skill in the art will understand that embodiments of theinvention are not limited to HEVC or VVC.

Encoder and Encoding Method

FIG. 2 shows a schematic block diagram of an example video encoder 20that is configured to implement the techniques of the presentapplication. In the example of FIG. 2, the video encoder 20 comprises aninput 201 (or input interface 201), a residual calculation unit 204, atransform processing unit 206, a quantization unit 208, an inversequantization unit 210, and inverse transform processing unit 212, areconstruction unit 214, a loop filter unit 220, a decoded picturebuffer (DPB) 230, a mode selection unit 260, an entropy encoding unit270 and an output 272 (or output interface 272). The mode selection unit260 may include an inter prediction unit 244, an intra prediction unit254 and a partitioning unit 262. Inter prediction unit 244 may include amotion estimation unit and a motion compensation unit (not shown). Avideo encoder 20 as shown in FIG. 2 may also be referred to as hybridvideo encoder or a video encoder according to a hybrid video codec.

The residual calculation unit 204, the transform processing unit 206,the quantization unit 208, the mode selection unit 260 may be referredto as forming a forward signal path of the encoder 20, whereas theinverse quantization unit 210, the inverse transform processing unit212, the reconstruction unit 214, the buffer 216, the loop filter 220,the decoded picture buffer (DPB) 230, the inter prediction unit 244 andthe intra-prediction unit 254 may be referred to as forming a backwardsignal path of the video encoder 20, wherein the backward signal path ofthe video encoder 20 corresponds to the signal path of the decoder (seevideo decoder 30 in FIG. 3). The inverse quantization unit 210, theinverse transform processing unit 212, the reconstruction unit 214, theloop filter 220, the decoded picture buffer (DPB) 230, the interprediction unit 244 and the intra-prediction unit 254 are also referredto forming the “built-in decoder” of video encoder 20.

Pictures & Picture Partitioning (Pictures & Blocks)

The encoder 20 may be configured to receive, e.g., via input 201, apicture 17 (or picture data 17), e.g., picture of a sequence of picturesforming a video or video sequence. The received picture or picture datamay also be a pre-processed picture 19 (or pre-processed picture data19). For sake of simplicity the following description refers to thepicture 17. The picture 17 may also be referred to as current picture orpicture to be coded (in particular in video coding to distinguish thecurrent picture from other pictures, e.g., previously encoded and/ordecoded pictures of the same video sequence, i.e. the video sequencewhich also comprises the current picture).

A (digital) picture is or can be regarded as a two-dimensional array ormatrix of samples with intensity values. A sample in the array may alsobe referred to as pixel (short form of picture element) or a pel. Thenumber of samples in horizontal and vertical direction (or axis) of thearray or picture define the size and/or resolution of the picture. Forrepresentation of color, typically three color components are employed,i.e. the picture may be represented or include three sample arrays. InRGB format or color space a picture comprises a corresponding red, greenand blue sample array. However, in video coding each pixel is typicallyrepresented in a luminance and chrominance format or color space, e.g.,YCbCr, which comprises a luminance component indicated by Y (sometimesalso L is used instead) and two chrominance components indicated by Cband Cr. The luminance (or short luma) component Y represents thebrightness or grey level intensity (e.g., like in a grey-scale picture),while the two chrominance (or short chroma) components Cb and Crrepresent the chromaticity or color information components. Accordingly,a picture in YCbCr format comprises a luminance sample array ofluminance sample values (Y), and two chrominance sample arrays ofchrominance values (Cb and Cr). Pictures in RGB format may be convertedor transformed into YCbCr format and vice versa, the process is alsoknown as color transformation or conversion. If a picture is monochrome,the picture may comprise only a luminance sample array. Accordingly, apicture may be, for example, an array of luma samples in monochromeformat or an array of luma samples and two corresponding arrays ofchroma samples in 4:2:0, 4:2:2, and 4:4:4 color format.

Embodiments of the video encoder 20 may comprise a picture partitioningunit (not depicted in FIG. 2) configured to partition the picture 17into a plurality of (typically non-overlapping) picture blocks 203.These blocks may also be referred to as root blocks, macro blocks(H.264/AVC) or coding tree blocks (CTB) or coding tree units (CTU)(H.265/HEVC and VVC). The picture partitioning unit may be configured touse the same block size for all pictures of a video sequence and thecorresponding grid defining the block size, or to change the block sizebetween pictures or subsets or groups of pictures, and partition eachpicture into the corresponding blocks.

In further embodiments, the video encoder may be configured to receivedirectly a block 203 of the picture 17, e.g., one, several or all blocksforming the picture 17. The picture block 203 may also be referred to ascurrent picture block or picture block to be coded.

Like the picture 17, the picture block 203 again is or can be regardedas a two-dimensional array or matrix of samples with intensity values(sample values), although of smaller dimension than the picture 17. Inother words, the block 203 may comprise, e.g., one sample array (e.g., aluma array in case of a monochrome picture 17, or a luma or chroma arrayin case of a color picture) or three sample arrays (e.g., a luma and twochroma arrays in case of a color picture 17) or any other number and/orkind of arrays depending on the color format applied. The number ofsamples in horizontal and vertical direction (or axis) of the block 203define the size of block 203. Accordingly, a block may, for example, anM×N (M-column by N-row) array of samples, or an M×N array of transformcoefficients.

Embodiments of the video encoder 20 as shown in FIG. 2 may be configuredencode the picture 17 block by block, e.g., the encoding and predictionis performed per block 203.

Residual Calculation

The residual calculation unit 204 may be configured to calculate aresidual block 205 (also referred to as residual 205) based on thepicture block 203 and a prediction block 265 (further details about theprediction block 265 are provided later), e.g., by subtracting samplevalues of the prediction block 265 from sample values of the pictureblock 203, sample by sample (pixel by pixel) to obtain the residualblock 205 in the sample domain.

Transform

The transform processing unit 206 may be configured to apply atransform, e.g., a discrete cosine transform (DCT) or discrete sinetransform (DST), on the sample values of the residual block 205 toobtain transform coefficients 207 in a transform domain. The transformcoefficients 207 may also be referred to as transform residualcoefficients and represent the residual block 205 in the transformdomain.

The transform processing unit 206 may be configured to apply integerapproximations of DCT/DST, such as the transforms specified forH.265/HEVC. Compared to an orthogonal DCT transform, such integerapproximations are typically scaled by a certain factor. In order topreserve the norm of the residual block which is processed by forwardand inverse transforms, additional scaling factors are applied as partof the transform process. The scaling factors are typically chosen basedon certain constraints like scaling factors being a power of two forshift operations, bit depth of the transform coefficients, tradeoffbetween accuracy and implementation costs, etc. Specific scaling factorsare, for example, specified for the inverse transform, e.g., by inversetransform processing unit 212 (and the corresponding inverse transform,e.g., by inverse transform processing unit 312 at video decoder 30) andcorresponding scaling factors for the forward transform, e.g., bytransform processing unit 206, at an encoder 20 may be specifiedaccordingly.

Embodiments of the video encoder 20 (respectively transform processingunit 206) may be configured to output transform parameters, e.g., a typeof transform or transforms, e.g., directly or encoded or compressed viathe entropy encoding unit 270, so that, e.g., the video decoder 30 mayreceive and use the transform parameters for decoding.

Quantization

The quantization unit 208 may be configured to quantize the transformcoefficients 207 to obtain quantized coefficients 209, e.g., by applyingscalar quantization or vector quantization. The quantized coefficients209 may also be referred to as quantized transform coefficients 209 orquantized residual coefficients 209.

The quantization process may reduce the bit depth associated with someor all of the transform coefficients 207. For example, an n-bittransform coefficient may be rounded down to an m-bit Transformcoefficient during quantization, where n is greater than m. The degreeof quantization may be modified by adjusting a quantization parameter(QP). For example for scalar quantization, different scaling may beapplied to achieve finer or coarser quantization. Smaller quantizationstep sizes correspond to finer quantization, whereas larger quantizationstep sizes correspond to coarser quantization. The applicablequantization step size may be indicated by a quantization parameter(QP). The quantization parameter may for example be an index to apredefined set of applicable quantization step sizes. For example, smallquantization parameters may correspond to fine quantization (smallquantization step sizes) and large quantization parameters maycorrespond to coarse quantization (large quantization step sizes) orvice versa. The quantization may include division by a quantization stepsize and a corresponding inverse quantization, e.g., by inversequantization unit 210, may include multiplication by the quantizationstep size. Embodiments according to some standards, e.g., HEVC, may beconfigured to use a quantization parameter to determine the quantizationstep size. Generally, the quantization step size may be calculated basedon a quantization parameter using a fixed point approximation of anequation including division. Additional scaling factors may beintroduced for quantization and dequantization to restore the norm ofthe residual block, which might get modified because of the scaling usedin the fixed point approximation of the equation for quantization stepsize and quantization parameter. In one example implementation, thescaling of the inverse transform and dequantization might be combined.Alternatively, customized quantization tables may be used and signaledfrom an encoder to a decoder, e.g., in a bitstream. The quantization isa lossy operation, wherein the loss increases with increasingquantization step sizes.

Embodiments of the video encoder 20 (respectively quantization unit 208)may be configured to output quantization parameters (QP), e.g., directlyor encoded via the entropy encoding unit 270, so that, e.g., the videodecoder 30 may receive and apply the quantization parameters fordecoding.

Inverse Quantization

The inverse quantization unit 210 is configured to apply the inversequantization of the quantization unit 208 on the quantized coefficientsto obtain dequantized coefficients 211, e.g., by applying the inverse ofthe quantization scheme applied by the quantization unit 208 based on orusing the same quantization step size as the quantization unit 208. Thedequantized coefficients 211 may also be referred to as dequantizedresidual coefficients 211 and correspond—although typically notidentical to the transform coefficients due to the loss byquantization—to the transform coefficients 207.

Inverse Transform

The inverse transform processing unit 212 is configured to apply theinverse transform of the transform applied by the transform processingunit 206, e.g., an inverse discrete cosine transform (DCT) or inversediscrete sine transform (DST) or other inverse transforms, to obtain areconstructed residual block 213 (or corresponding dequantizedcoefficients 213) in the sample domain. The reconstructed residual block213 may also be referred to as transform block 213.

Reconstruction

The reconstruction unit 214 (e.g., adder or summer 214) is configured toadd the transform block 213 (i.e. reconstructed residual block 213) tothe prediction block 265 to obtain a reconstructed block 215 in thesample domain, e.g., by adding—sample by sample—the sample values of thereconstructed residual block 213 and the sample values of the predictionblock 265.

Filtering

The loop filter unit 220 (or short “loop filter” 220), is configured tofilter the reconstructed block 215 to obtain a filtered block 221, or ingeneral, to filter reconstructed samples to obtain filtered samples. Theloop filter unit is, e.g., configured to smooth pixel transitions, orotherwise improve the video quality. The loop filter unit 220 maycomprise one or more loop filters such as a de-blocking filter, asample-adaptive offset (SAO) filter or one or more other filters, e.g.,a bilateral filter, an adaptive loop filter (ALF), a sharpening, asmoothing filters or a collaborative filters, or any combinationthereof. Although the loop filter unit 220 is shown in FIG. 2 as beingan in loop filter, in other configurations, the loop filter unit 220 maybe implemented as a post loop filter. The filtered block 221 may also bereferred to as filtered reconstructed block 221. Decoded picture buffer230 may store the reconstructed coding blocks after the loop filter unit220 performs the filtering operations on the reconstructed codingblocks.

Embodiments of the video encoder 20 (respectively loop filter unit 220)may be configured to output loop filter parameters (such as sampleadaptive offset information), e.g., directly or encoded via the entropyencoding unit 270, so that, e.g., a decoder 30 may receive and apply thesame loop filter parameters or respective loop filters for decoding.

Decoded Picture Buffer

The decoded picture buffer (DPB) 230 may be a memory that storesreference pictures, or in general reference picture data, for encodingvideo data by video encoder 20. The DPB 230 may be formed by any of avariety of memory devices, such as dynamic random access memory (DRAM),including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM),resistive RAM (RRAM), or other types of memory devices. The decodedpicture buffer (DPB) 230 may be configured to store one or more filteredblocks 221. The decoded picture buffer 230 may be further configured tostore other previously filtered blocks, e.g., previously reconstructedand filtered blocks 221, of the same current picture or of differentpictures, e.g., previously reconstructed pictures, and may providecomplete previously reconstructed, i.e. decoded, pictures (andcorresponding reference blocks and samples) and/or a partiallyreconstructed current picture (and corresponding reference blocks andsamples), for example for inter prediction. The decoded picture buffer(DPB) 230 may be also configured to store one or more unfilteredreconstructed blocks 215, or in general unfiltered reconstructedsamples, e.g., if the reconstructed block 215 is not filtered by loopfilter unit 220, or any other further processed version of thereconstructed blocks or samples.

Mode Selection (Partitioning & Prediction)

The mode selection unit 260 comprises partitioning unit 262,inter-prediction unit 244 and intra-prediction unit 254, and isconfigured to receive or obtain original picture data, e.g., an originalblock 203 (current block 203 of the current picture 17), andreconstructed picture data, e.g., filtered and/or unfilteredreconstructed samples or blocks of the same (current) picture and/orfrom one or a plurality of previously decoded pictures, e.g., fromdecoded picture buffer 230 or other buffers (e.g., line buffer, notshown). The reconstructed picture data is used as reference picture datafor prediction, e.g., inter-prediction or intra-prediction, to obtain aprediction block 265 or predictor 265.

Mode selection unit 260 may be configured to determine or select apartitioning for a current block prediction mode (including nopartitioning) and a prediction mode (e.g., an intra or inter predictionmode) and generate a corresponding prediction block 265, which is usedfor the calculation of the residual block 205 and for the reconstructionof the reconstructed block 215.

Embodiments of the mode selection unit 260 may be configured to selectthe partitioning and the prediction mode (e.g., from those supported byor available for mode selection unit 260), which provide the best matchor in other words the minimum residual (minimum residual means bettercompression for transmission or storage), or a minimum signalingoverhead (minimum signaling overhead means better compression fortransmission or storage), or which considers or balances both. The modeselection unit 260 may be configured to determine the partitioning andprediction mode based on rate distortion optimization (RDO), i.e. selectthe prediction mode which provides a minimum rate distortion. Terms like“best”, “minimum”, “optimum” etc. in this context do not necessarilyrefer to an overall “best”, “minimum”, “optimum”, etc. but may alsorefer to the fulfillment of a termination or selection criterion like avalue exceeding or falling below a threshold or other constraintsleading potentially to a “sub-optimum selection” but reducing complexityand processing time.

In other words, the partitioning unit 262 may be configured to partitionthe block 203 into smaller block partitions or sub-blocks (which formagain blocks), e.g., iteratively using quad-tree-partitioning (QT),binary partitioning (BT) or triple-tree-partitioning (TT) or anycombination thereof, and to perform, e.g., the prediction for each ofthe block partitions or sub-blocks, wherein the mode selection comprisesthe selection of the tree-structure of the partitioned block 203 and theprediction modes are applied to each of the block partitions orsub-blocks.

In the following the partitioning (e.g., by partitioning unit 260) andprediction processing (by inter-prediction unit 244 and intra-predictionunit 254) performed by an example video encoder 20 will be explained inmore detail.

Partitioning

The partitioning unit 262 may partition (or split) a current block 203into smaller partitions, e.g., smaller blocks of square or rectangularsize. These smaller blocks (which may also be referred to as sub-blocks)may be further partitioned into even smaller partitions. This is alsoreferred to tree-partitioning or hierarchical tree-partitioning, whereina root block, e.g., at root tree-level 0 (hierarchy-level 0, depth 0),may be recursively partitioned, e.g., partitioned into two or moreblocks of a next lower tree-level, e.g., nodes at tree-level 1(hierarchy-level 1, depth 1), wherein these blocks may be againpartitioned into two or more blocks of a next lower level, e.g.,tree-level 2 (hierarchy-level 2, depth 2), etc. until the partitioningis terminated, e.g., because a termination criterion is fulfilled, e.g.,a maximum tree depth or minimum block size is reached. Blocks which arenot further partitioned are also referred to as leaf-blocks or leafnodes of the tree. A tree using partitioning into two partitions isreferred to as binary-tree (BT), a tree using partitioning into threepartitions is referred to as ternary-tree (TT), and a tree usingpartitioning into four partitions is referred to as quad-tree (QT).

As mentioned before, the term “block” as used herein may be a portion,in particular a square or rectangular portion, of a picture. Withreference, for example, to HEVC and VVC, the block may be or correspondto a coding tree unit (CTU), a coding unit (CU), prediction unit (PU),and transform unit (TU) and/or to the corresponding blocks, e.g., acoding tree block (CTB), a coding block (CB), a transform block (TB) orprediction block (PB).

For example, a coding tree unit (CTU) may be or comprise a CTB of lumasamples, two corresponding CTBs of chroma samples of a picture that hasthree sample arrays, or a CTB of samples of a monochrome picture or apicture that is coded using three separate colour planes and syntaxstructures used to code the samples. Correspondingly, a coding treeblock (CTB) may be an N×N block of samples for some value of N such thatthe division of a component into CTBs is a partitioning. A coding unit(CU) may be or comprise a coding block of luma samples, twocorresponding coding blocks of chroma samples of a picture that hasthree sample arrays, or a coding block of samples of a monochromepicture or a picture that is coded using three separate color planes andsyntax structures used to code the samples. Correspondingly a codingblock (CB) may be an M×N block of samples for some values of M and Nsuch that the division of a CTB into coding blocks is a partitioning.

In embodiments, e.g., according to HEVC, a coding tree unit (CTU) may besplit into CUs by using a quad-tree structure denoted as coding tree.The decision whether to code a picture area using inter-picture(temporal) or intra-picture (spatial) prediction is made at the CUlevel. Each CU can be further split into one, two or four PUs accordingto the PU splitting type. Inside one PU, the same prediction process isapplied and the relevant information is transmitted to the decoder on aPU basis. After obtaining the residual block by applying the predictionprocess based on the PU splitting type, a CU can be partitioned intotransform units (TUs) according to another quadtree structure similar tothe coding tree for the CU.

In embodiments, e.g., according to the latest video coding standardcurrently in development, which is referred to as Versatile Video Coding(VVC), Quad-tree and binary tree (QTBT) partitioning is used topartition a coding block. In the QTBT block structure, a CU can haveeither a square or rectangular shape. For example, a coding tree unit(CTU) is first partitioned by a quadtree structure. The quadtree leafnodes are further partitioned by a binary tree or ternary (or triple)tree structure. The partitioning tree leaf nodes are called coding units(CUs), and that segmentation is used for prediction and transformprocessing without any further partitioning. This means that the CU, PUand TU have the same block size in the QTBT coding block structure. Inparallel, multiple partition, for example, triple tree partition wasalso proposed to be used together with the QTBT block structure.

In one example, the mode selection unit 260 of video encoder 20 may beconfigured to perform any combination of the partitioning techniquesdescribed herein.

As described above, the video encoder 20 is configured to determine orselect the best or an optimum prediction mode from a set of(pre-determined) prediction modes. The set of prediction modes maycomprise, e.g., intra-prediction modes and/or inter-prediction modes.

Intra-Prediction

The set of intra-prediction modes may comprise 35 differentintra-prediction modes, e.g., non-directional modes like DC (or mean)mode and planar mode, or directional modes, e.g., as defined in HEVC, ormay comprise 67 different intra-prediction modes, e.g., non-directionalmodes like DC (or mean) mode and planar mode, or directional modes,e.g., as defined for VVC.

The intra-prediction unit 254 is configured to use reconstructed samplesof neighboring blocks of the same current picture to generate anintra-prediction block 265 according to an intra-prediction mode of theset of intra-prediction modes.

The intra prediction unit 254 (or in general the mode selection unit260) is further configured to output intra-prediction parameters (or ingeneral information indicative of the selected intra prediction mode forthe block) to the entropy encoding unit 270 in form of syntax elements266 for inclusion into the encoded picture data 21, so that, e.g., thevideo decoder 30 may receive and use the prediction parameters fordecoding.

Inter-Prediction

The set of (or possible) inter-prediction modes depends on the availablereference pictures (i.e. previous at least partially decoded pictures,e.g., stored in DPB 230) and other inter-prediction parameters, e.g.,whether the whole reference picture or only a part, e.g., a searchwindow area around the area of the current block, of the referencepicture is used for searching for a best matching reference block,and/or e.g., whether pixel interpolation is applied, e.g., half/semi-peland/or quarter-pel interpolation, or not.

Additional to the above prediction modes, skip mode and/or direct modemay be applied.

The inter prediction unit 244 may include a motion estimation (ME) unitand a motion compensation (MC) unit (both not shown in FIG. 2). Themotion estimation unit may be configured to receive or obtain thepicture block 203 (current picture block 203 of the current picture 17)and a decoded picture 231, or at least one or a plurality of previouslyreconstructed blocks, e.g., reconstructed blocks of one or a pluralityof other/different previously decoded pictures 231, for motionestimation. E.g., a video sequence may comprise the current picture andthe previously decoded pictures 231, or in other words, the currentpicture and the previously decoded pictures 231 may be part of or form asequence of pictures forming a video sequence.

The encoder 20 may, e.g., be configured to select a reference block froma plurality of reference blocks of the same or different pictures of theplurality of other pictures and provide a reference picture (orreference picture index) and/or an offset (spatial offset) between theposition (x, y coordinates) of the reference block and the position ofthe current block as inter prediction parameters to the motionestimation unit. This offset is also called motion vector (MV).

The motion compensation unit is configured to obtain, e.g., receive, aninter prediction parameter and to perform inter prediction based on orusing the inter prediction parameter to obtain an inter prediction block265. Motion compensation, performed by the motion compensation unit, mayinvolve fetching or generating the prediction block based on themotion/block vector determined by motion estimation, possibly performinginterpolations to sub-pixel precision. Interpolation filtering maygenerate additional pixel samples from known pixel samples, thuspotentially increasing the number of candidate prediction blocks thatmay be used to code a picture block. Upon receiving the motion vectorfor the PU of the current picture block, the motion compensation unitmay locate the prediction block to which the motion vector points in oneof the reference picture lists.

Motion compensation unit may also generate syntax elements associatedwith the blocks and the video slice for use by video decoder 30 indecoding the picture blocks of the video slice.

Entropy Coding

The entropy encoding unit 270 is configured to apply, for example, anentropy encoding algorithm or scheme (e.g., a variable length coding(VLC) scheme, an context adaptive VLC scheme (CAVLC), an arithmeticcoding scheme, a binarization, a context adaptive binary arithmeticcoding (CABAC), syntax-based context-adaptive binary arithmetic coding(SBAC), probability interval partitioning entropy (PIPE) coding oranother entropy encoding methodology or technique) or bypass (nocompression) on the quantized coefficients 209, inter predictionparameters, intra prediction parameters, loop filter parameters and/orother syntax elements to obtain encoded picture data 21 which can beoutput via the output 272, e.g., in the form of an encoded bitstream 21,so that, e.g., the video decoder 30 may receive and use the parametersfor decoding. The encoded bitstream 21 may be transmitted to videodecoder 30, or stored in a memory for later transmission or retrieval byvideo decoder 30.

Other structural variations of the video encoder 20 can be used toencode the video stream. For example, a non-transform based encoder 20can quantize the residual signal directly without the transformprocessing unit 206 for certain blocks or frames. In anotherimplementation, an encoder 20 can have the quantization unit 208 and theinverse quantization unit 210 combined into a single unit.

Decoder and Decoding Method

FIG. 3 shows an example of a video decoder 30 that is configured toimplement the techniques of this present application. The video decoder30 is configured to receive encoded picture data 21 (e.g., encodedbitstream 21), e.g., encoded by encoder 20, to obtain a decoded picture331. The encoded picture data or bitstream comprises information fordecoding the encoded picture data, e.g., data that represents pictureblocks of an encoded video slice and associated syntax elements.

In the example of FIG. 3, the decoder 30 comprises an entropy decodingunit 304, an inverse quantization unit 310, an inverse transformprocessing unit 312, a reconstruction unit 314 (e.g., a summer 314), aloop filter 320, a decoded picture buffer (DBP) 330, an inter predictionunit 344 and an intra prediction unit 354. Inter prediction unit 344 maybe or include a motion compensation unit. Video decoder 30 may, in someexamples, perform a decoding pass generally reciprocal to the encodingpass described with respect to video encoder 100 from FIG. 2.

As explained with regard to the encoder 20, the inverse quantizationunit 210, the inverse transform processing unit 212, the reconstructionunit 214 the loop filter 220, the decoded picture buffer (DPB) 230, theinter prediction unit 344 and the intra prediction unit 354 are alsoreferred to as forming the “built-in decoder” of video encoder 20.Accordingly, the inverse quantization unit 310 may be identical infunction to the inverse quantization unit 110, the inverse transformprocessing unit 312 may be identical in function to the inversetransform processing unit 212, the reconstruction unit 314 may beidentical in function to reconstruction unit 214, the loop filter 320may be identical in function to the loop filter 220, and the decodedpicture buffer 330 may be identical in function to the decoded picturebuffer 230. Therefore, the explanations provided for the respectiveunits and functions of the video 20 encoder apply correspondingly to therespective units and functions of the video decoder 30.

Entropy Decoding

The entropy decoding unit 304 is configured to parse the bitstream 21(or in general encoded picture data 21) and perform, for example,entropy decoding to the encoded picture data 21 to obtain, e.g.,quantized coefficients 309 and/or decoded coding parameters (not shownin FIG. 3), e.g., any or all of inter prediction parameters (e.g.,reference picture index and motion vector), intra prediction parameter(e.g., intra prediction mode or index), transform parameters,quantization parameters, loop filter parameters, and/or other syntaxelements. Entropy decoding unit 304 maybe configured to apply thedecoding algorithms or schemes corresponding to the encoding schemes asdescribed with regard to the entropy encoding unit 270 of the encoder20. Entropy decoding unit 304 may be further configured to provide interprediction parameters, intra prediction parameter and/or other syntaxelements to the mode selection unit 360 and other parameters to otherunits of the decoder 30. Video decoder 30 may receive the syntaxelements at the video slice level and/or the video block level.

Inverse Quantization

The inverse quantization unit 310 may be configured to receivequantization parameters (QP) (or in general information related to theinverse quantization) and quantized coefficients from the encodedpicture data 21 (e.g., by parsing and/or decoding, e.g., by entropydecoding unit 304) and to apply based on the quantization parameters aninverse quantization on the decoded quantized coefficients 309 to obtaindequantized coefficients 311, which may also be referred to as transformcoefficients 311. The inverse quantization process may include use of aquantization parameter determined by video encoder 20 for each videoblock in the video slice to determine a degree of quantization and,likewise, a degree of inverse quantization that should be applied.

Inverse Transform

Inverse transform processing unit 312 may be configured to receivedequantized coefficients 311, also referred to as transform coefficients311, and to apply a transform to the dequantized coefficients 311 inorder to obtain reconstructed residual blocks 213 in the sample domain.The reconstructed residual blocks 213 may also be referred to astransform blocks 313. The transform may be an inverse transform, e.g.,an inverse DCT, an inverse DST, an inverse integer transform, or aconceptually similar inverse transform process. The inverse transformprocessing unit 312 may be further configured to receive transformparameters or corresponding information from the encoded picture data 21(e.g., by parsing and/or decoding, e.g., by entropy decoding unit 304)to determine the transform to be applied to the dequantized coefficients311.

Reconstruction

The reconstruction unit 314 (e.g., adder or summer 314) may beconfigured to add the reconstructed residual block 313, to theprediction block 365 to obtain a reconstructed block 315 in the sampledomain, e.g., by adding the sample values of the reconstructed residualblock 313 and the sample values of the prediction block 365.

Filtering

The loop filter unit 320 (either in the coding loop or after the codingloop) is configured to filter the reconstructed block 315 to obtain afiltered block 321, e.g., to smooth pixel transitions, or otherwiseimprove the video quality. The loop filter unit 320 may comprise one ormore loop filters such as a de-blocking filter, a sample-adaptive offset(SAO) filter or one or more other filters, e.g., a bilateral filter, anadaptive loop filter (ALF), a sharpening, a smoothing filters or acollaborative filters, or any combination thereof. Although the loopfilter unit 320 is shown in FIG. 3 as being an in loop filter, in otherconfigurations, the loop filter unit 320 may be implemented as a postloop filter.

Decoded Picture Buffer

The decoded video blocks 321 of a picture are then stored in decodedpicture buffer 330, which stores the decoded pictures 331 as referencepictures for subsequent motion compensation for other pictures and/orfor output respectively display.

The decoder 30 is configured to output the decoded picture 311, e.g.,via output 312, for presentation or viewing to a user.

Prediction

The inter prediction unit 344 may be identical to the inter predictionunit 244 (in particular to the motion compensation unit) and the intraprediction unit 354 may be identical to the inter prediction unit 254 infunction, and performs split or partitioning decisions and predictionbased on the partitioning and/or prediction parameters or respectiveinformation received from the encoded picture data 21 (e.g., by parsingand/or decoding, e.g., by entropy decoding unit 304). Mode selectionunit 360 may be configured to perform the prediction (intra or interprediction) per block based on reconstructed pictures, blocks orrespective samples (filtered or unfiltered) to obtain the predictionblock 365.

When the video slice is coded as an intra coded (I) slice, intraprediction unit 354 of mode selection unit 360 is configured to generateprediction block 365 for a picture block of the current video slicebased on a signaled intra prediction mode and data from previouslydecoded blocks of the current picture. When the video picture is codedas an inter coded (i.e., B, or P) slice, inter prediction unit 344(e.g., motion compensation unit) of mode selection unit 360 isconfigured to produce prediction blocks 365 for a video block of thecurrent video slice based on the motion vectors and other syntaxelements received from entropy decoding unit 304. For inter prediction,the prediction blocks may be produced from one of the reference pictureswithin one of the reference picture lists. Video decoder 30 mayconstruct the reference frame lists, List 0 and List 1, using defaultconstruction techniques based on reference pictures stored in DPB 330.

Mode selection unit 360 is configured to determine the predictioninformation for a video block of the current video slice by parsing themotion vectors and other syntax elements, and uses the predictioninformation to produce the prediction blocks for the current video blockbeing decoded. For example, the mode selection unit 360 uses some of thereceived syntax elements to determine a prediction mode (e.g., intra orinter prediction) used to code the video blocks of the video slice, aninter prediction slice type (e.g., B slice, P slice, or GPB slice),construction information for one or more of the reference picture listsfor the slice, motion vectors for each inter encoded video block of theslice, inter prediction status for each inter coded video block of theslice, and other information to decode the video blocks in the currentvideo slice.

Other variations of the video decoder 30 can be used to decode theencoded picture data 21. For example, the decoder 30 can produce theoutput video stream without the loop filtering unit 320. For example, anon-transform based decoder 30 can inverse-quantize the residual signaldirectly without the inverse-transform processing unit 312 for certainblocks or frames. In another implementation, the video decoder 30 canhave the inverse-quantization unit 310 and the inverse-transformprocessing unit 312 combined into a single unit.

FIG. 4 is a schematic diagram of a video coding device 400 according toan embodiment of the disclosure. The video coding device 400 is suitablefor implementing the disclosed embodiments as described herein. In anembodiment, the video coding device 400 may be a decoder such as videodecoder 30 of FIG. 1A or an encoder such as video encoder 20 of FIG. 1A.

The video coding device 400 comprises ingress ports 410 (or input ports410) and receiver units (Rx) 420 for receiving data; a processor, logicunit, or central processing unit (CPU) 430 to process the data;transmitter units (Tx) 440 and egress ports 450 (or output ports 450)for transmitting the data; and a memory 460 for storing the data. Thevideo coding device 400 may also comprise optical-to-electrical (OE)components and electrical-to-optical (EO) components coupled to theingress ports 410, the receiver units 420, the transmitter units 440,and the egress ports 450 for egress or ingress of optical or electricalsignals.

The processor 430 is implemented by hardware and software. The processor430 may be implemented as one or more CPU chips, cores (e.g., as amulti-core processor), FPGAs, ASICs, and DSPs. The processor 430 is incommunication with the ingress ports 410, receiver units 420,transmitter units 440, egress ports 450, and memory 460. The processor430 comprises a coding module 470. The coding module 470 implements thedisclosed embodiments described above. For instance, the coding module470 implements, processes, prepares, or provides the various codingoperations. The inclusion of the coding module 470 therefore provides asubstantial improvement to the functionality of the video coding device400 and effects a transformation of the video coding device 400 to adifferent state. Alternatively, the coding module 470 is implemented asinstructions stored in the memory 460 and executed by the processor 430.

The memory 460 may comprise one or more disks, tape drives, andsolid-state drives and may be used as an over-flow data storage device,to store programs when such programs are selected for execution, and tostore instructions and data that are read during program execution. Thememory 460 may be, for example, volatile and/or non-volatile and may bea read-only memory (ROM), random access memory (RAM), ternarycontent-addressable memory (TCAM), and/or static random-access memory(SRAM).

FIG. 5 is a simplified block diagram of an apparatus 500 that may beused as either or both of the source device 12 and the destinationdevice 14 from FIG. 1A according to an exemplary embodiment. Theapparatus 500 can implement techniques of this present applicationdescribed above. The apparatus 500 can be in the form of a computingsystem including multiple computing devices, or in the form of a singlecomputing device, for example, a mobile phone, a tablet computer, alaptop computer, a notebook computer, a desktop computer, and the like.

A processor 502 in the apparatus 500 can be a central processing unit.Alternatively, the processor 502 can be any other type of device, ormultiple devices, capable of manipulating or processing informationnow-existing or hereafter developed. Although the disclosedimplementations can be practiced with a single processor as shown, e.g.,the processor 502, advantages in speed and efficiency can be achievedusing more than one processor.

A memory 504 in the apparatus 500 can be a read only memory (ROM) deviceor a random access memory (RAM) device in an implementation. Any othersuitable type of storage device can be used as the memory 504. Thememory 504 can include code and data 506 that is accessed by theprocessor 502 using a bus 512. The memory 504 can further include anoperating system 508 and application programs 510, the applicationprograms 510 including at least one program that permits the processor502 to perform the methods described here. For example, the applicationprograms 510 can include applications 1 through N, which further includea video coding application that performs the methods described here. Theapparatus 500 can also include additional memory in the form of asecondary storage 514, which can, for example, be a memory card usedwith a mobile computing device. Because the video communication sessionsmay contain a significant amount of information, they can be stored inwhole or in part in the secondary storage 514 and loaded into the memory504 as needed for processing.

The apparatus 500 can also include one or more output devices, such as adisplay 518. The display 518 may be, in one example, a touch sensitivedisplay that combines a display with a touch sensitive element that isoperable to sense touch inputs. The display 518 can be coupled to theprocessor 502 via the bus 512. Other output devices that permit a userto program or otherwise use the apparatus 500 can be provided inaddition to or as an alternative to the display 518. When the outputdevice is or includes a display, the display can be implemented invarious ways, including by a liquid crystal display (LCD), a cathode-raytube (CRT) display, a plasma display or light emitting diode (LED)display, such as an organic LED (OLED) display.

The apparatus 500 can also include or be in communication with animage-sensing device 520, for example a camera, or any otherimage-sensing device 520 now existing or hereafter developed that cansense an image such as the image of a user operating the apparatus 500.The image-sensing device 520 can be positioned such that it is directedtoward the user operating the apparatus 500. In an example, the positionand optical axis of the image-sensing device 520 can be configured suchthat the field of vision includes an area that is directly adjacent tothe display 518 and from which the display 518 is visible.

The apparatus 500 can also include or be in communication with asound-sensing device 522, for example a microphone, or any othersound-sensing device now existing or hereafter developed that can sensesounds near the apparatus 500. The sound-sensing device 522 can bepositioned such that it is directed toward the user operating theapparatus 500 and can be configured to receive sounds, for example,speech or other utterances, made by the user while the user operates theapparatus 500.

Although FIG. 5 depicts the processor 502 and the memory 504 of theapparatus 500 as being integrated into a single unit, otherconfigurations can be utilized. The operations of the processor 502 canbe distributed across multiple machines (each machine having one or moreof processors) that can be coupled directly or across a local area orother network. The memory 504 can be distributed across multiplemachines such as a network-based memory or memory in multiple machinesperforming the operations of the apparatus 500. Although depicted hereas a single bus, the bus 512 of the apparatus 500 can be composed ofmultiple buses. Further, the secondary storage 514 can be directlycoupled to the other components of the apparatus 500 or can be accessedvia a network and can comprise a single integrated unit such as a memorycard or multiple units such as multiple memory cards. The apparatus 500can thus be implemented in a wide variety of configurations.

Video coding schemes such as H.264/AVC and HEVC are designed along thesuccessful principle of block-based hybrid video coding. Using thisprinciple a picture is first partitioned into blocks and then each blockis predicted by using intra-picture or inter-picture prediction.

As used herein, the term “block” may a portion of a picture or a frame.For convenience of description, embodiments of the invention aredescribed herein in reference to High-Efficiency Video Coding (HEVC) orthe reference software of Versatile video coding (VVC), developed by theJoint Collaboration Team on Video Coding (JCT-VC) of ITU-T Video CodingExperts Group (VCEG) and ISO/IEC Motion Picture Experts Group (MPEG).One of ordinary skill in the art will understand that embodiments of theinvention are not limited to HEVC or VVC. It may refer to a CU, PU, andTU. In HEVC, a CTU is split into CUs by using a quad-tree structuredenoted as coding tree. The decision whether to code a picture areausing inter-picture (temporal) or intra-picture (spatial) prediction ismade at the CU level. Each CU can be further split into one, two or fourPUs according to the PU splitting type. Inside one PU, the sameprediction process is applied and the relevant information istransmitted to the decoder on a PU basis. After obtaining the residualblock by applying the prediction process based on the PU splitting type,a CU can be partitioned into transform units (TUs) according to anotherquadtree structure similar to the coding tree for the CU. In the newestdevelopment of the video compression technical, Quad-tree and binarytree (QTBT) partitioning is used to partition a coding block. In theQTBT block structure, a CU can have either a square or rectangularshape. For example, a coding tree unit (CTU) is first partitioned by aquadtree structure. The quadtree leaf nodes are further partitioned by abinary tree structure. The binary tree leaf nodes are called codingunits (CUs), and that segmentation is used for prediction and transformprocessing without any further partitioning. This means that the CU, PUand TU have the same block size in the QTBT coding block structure. Inparallel, multiple partition, for example, triple tree partition wasalso proposed to be used together with the QTBT block structure.

ITU-T VCEG (Q6/16) and ISO/IEC MPEG (JTC 1/SC 29/WG 11) are studying thepotential need for standardization of future video coding technologywith a compression capability that significantly exceeds that of thecurrent HEVC standard (including its current extensions and near-termextensions for screen content coding and high-dynamic-range coding). Thegroups are working together on this exploration activity in a jointcollaboration effort known as the Joint Video Exploration Team (JVET) toevaluate compression technology designs proposed by their experts inthis area.

For directional intra prediction, intra prediction modes are availablerepresenting different prediction angles from diagonal-up todiagonal-down. For definition of the prediction angles, an offset valuep_(ang) on a 32-sample grid is defined. The association of p_(ang) tothe corresponding intra prediction mode is visualized in FIG. 6 for thevertical prediction modes. For the horizontal prediction modes thescheme is flipped to vertical direction and the p_(ang) values areassigned accordingly. As stated above, all angular prediction modes areavailable for all applicable intra prediction block sizes. They all usethe same 32-sample grid for the definition of the prediction angles. Thedistribution of the p_(ang) values over the 32-sample grid in FIG. 6reveals an increased resolution of the prediction angles around thevertical direction and a coarser resolution of the prediction anglestowards the diagonal directions. The same applies to the horizontaldirections. This design stems from the observation that in lots of videocontent, approximately horizontal and vertical structures play animportant role compared to diagonal structures.

While for the horizontal and vertical prediction directions, theselection of samples to be used for prediction is straightforward, thistask requires more effort in case of angular prediction. For modes11-25, when predicting the current block Bc from the set of predictionsamples p_(ref) (also known as main reference side) in an angulardirection, samples of both, the vertical and the horizontal part ofp_(ref) can be involved. Since the determination of the location of therespective samples on either of the branches of p_(ref) requires somecomputational effort, a unified one-dimensional prediction reference hasbeen designed for HEVC intra prediction. The scheme is visualized inFIG. 7. Before performing the actual prediction operation, the set ofreference samples p_(ref) is mapped to a 1-dimensional vector p_(1,ref).The projection which is used for the mapping depends on the directionindicated by the intra prediction angle of the respective intraprediction mode. Only reference samples from the part of p_(ref) whichis to be used for prediction are mapped to p_(1,ref). The actual mappingof the reference samples to p_(1,ref) for each angular prediction modeis depicted in FIGS. 8 and 9 for horizontal and vertical angularprediction directions, respectively. The reference samples set p_(1,ref)is constructed once for the predicted block. The prediction is thenderived from two neighboring reference samples in the set as detailedbelow. As can be seen from FIGS. 8 and 9 the 1-dimensional referencesample set is not completely filled for all intra prediction modes. Onlythe locations which are in the projection range for the correspondingintra prediction direction are included in the set.

The prediction for both, horizontal and vertical prediction modes isperformed in the same manner with only swapping the x and y coordinatesof the block. The prediction from p_(1,ref) is performed in 1/32-pelaccuracy. Depending on the value of the angle parameter pang, a sampleoffset i_(idx) in p_(1,ref) and a weighting factor/fact for a sample atposition (x, y) are determined. Here, the derivation for the verticalmodes is provided. The derivation for the horizontal modes followsaccordingly, swapping x and y.

${i_{idx} = {\left( {y + 1} \right) \cdot \frac{p_{ang}}{32}}},{i_{fact} = {\left\lbrack {\left( {y + 1} \right) \cdot p_{ang}} \right\rbrack{mod}\; 32.}}$

If i_(fact) is not equal to 0, i.e. the prediction does not fall exactlyon a full sample location in p 1,ref, a linear weighting between the twoneighboring sample locations in p_(1,ref) is performed as

${{B_{c}\left( {x,y} \right)} = {{\frac{32 - i_{fact}}{32} \cdot {p_{1.{ref}}\left( {x + i_{idx} + 1} \right)}} + {\frac{i_{fact}}{32} \cdot {p_{1.{ref}}\left( {x + i_{idx} + 2} \right)}}}},$

with 0≤x, y<Nc. It should be noted that the values of i_(idx) andi_(fact) only depend on y and therefore only need to be calculated onceper row (for vertical prediction modes).

The VTM-1.0 (Versatile Test Model) uses 35 Intra modes whereas the BMS(Benchmark Set) uses 67 Intra modes. Intra-prediction is a mechanismused in many video coding frameworks to increase compression efficiencyin the cases where only a given frame can be involved.

FIG. 10A shows an example of 67 intra prediction modes, e.g., asproposed for VVC, the plurality of intra prediction modes of 67 intraprediction modes comprising: planar mode (index 0), dc mode (index 1),and angular modes with indices 2 to 66, wherein the left bottom angularmode in FIG. 10A refers to index 2 and the numbering of the indicesbeing incremented until index 66 being the top right most angular modeof FIG. 10A.

As shown in FIGS. 10B-10C, the latest version of JEM has some modescorresponding to skew intra prediction directions. For any of thesemodes, to predict samples within a block interpolation of a set ofneighboring reference samples should be performed, if a correspondingposition within a block side is fractional. HEVC and VVC uses linearinterpolation between two adjacent reference samples. JEM uses moresophisticated 4-tap interpolation filters. Filter coefficients areselected to be either Gaussian or Cubic ones depending on the width oron the height value. Decision on whether to use width or height isharmonized with the decision on main reference side selection: whenintra prediction mode is greater or equal to diagonal mode, top side ofreference samples is selected to be the main reference side and widthvalue is selected to determine interpolation filter in use. Otherwise,main reference side is selected from the left side of the block andheight controls the filter selection process. Specifically, if selectedside length is smaller than or equal to 8 samples, Cubic interpolation 4tap is applied. Otherwise, interpolation filter is a 4-tap Gaussian one.

Specific filter coefficient used in JEM are given in Table 1. Predictedsample is calculated by convoluting with coefficients selected fromTable 1 according to subpixel offset and filter type as follows:

s(x)=(Σ_(i=0) ^(i<4)(ref_(i+x) ·c _(i))+128)>>8

In this equation, “>>” indicates a bitwise shift-right operation.

If Cubic filter is selected, predicted sample is further clipped to theallowed range of values, that is either defined in SPS or derived fromthe bit depth of the selected component.

TABLE 1 Intra prediction interpolation filters used in JEM SubpixelCubic filter Gauss filter offset c₀ c₁ c₂ c₃ c₀ c₁ c₂ c₃ 0 (integer) 0256 0 0 47 161 47 1 1 −3 252 8 −1 43 161 51 1 2 −5 247 17 −3 40 160 54 23 −7 242 25 −4 37 159 58 2 4 −9 236 34 −5 34 158 62 2 5 −10 230 43 −7 31156 67 2 6 −12 224 52 −8 28 154 71 3 7 −13 217 61 −9 26 151 76 3 8 −14210 70 −10 23 149 80 4 9 −15 203 79 −11 21 146 85 4 10 −16 195 89 −12 19142 90 5 11 −16 187 98 −13 17 139 94 6 12 −16 179 107 −14 16 135 99 6 13−16 170 116 −14 14 131 104 7 14 −17 162 126 −15 13 127 108 8 15 −16 153135 −16 11 123 113 9 16 (half-pel) −16 144 144 −16 10 118 118 10 17 −16135 153 −16 9 113 123 11 18 −15 126 162 −17 8 108 127 13 19 −14 116 170−16 7 104 131 14 20 −14 107 179 −16 6 99 135 16 21 −13 98 187 −16 6 94139 17 22 −12 89 195 −16 5 90 142 19 23 −11 79 203 −15 4 85 146 21 24−10 70 210 −14 4 80 149 23 25 −9 61 217 −13 3 76 151 26 26 −8 52 224 −123 71 154 28 27 −7 43 230 −10 2 67 156 31 28 −5 34 236 −9 2 62 158 34 29−4 25 242 −7 2 58 159 37 30 −3 17 247 −5 2 54 160 40 31 −1 8 252 −3 1 51161 43

Another set of interpolation filters that have 6-bit precision ispresented in Table 2.

TABLE 2 A set of interpolation filters with 6-bit precision Unifiedintra/inter Subpixel filter Gaussian filter offset c₀ c₁ c₂ c₃ c₀ c₁ c₂c₃ 0 (integer) 0 64 0 0 16 32 16 0 1 −1 63 2 0 15 29 17 3 2 −2 62 4 0 1429 18 3 3 −2 60 7 −1 14 29 18 3 4 −2 58 10 −2 14 28 18 4 5 −3 57 12 −213 28 19 4 6 −4 56 14 −2 12 28 20 4 7 −4 55 15 −2 12 27 20 5 8 −4 54 16−2 11 27 21 5 9 −5 53 18 −2 11 27 21 5 10 −6 52 20 −2 10 26 22 6 11 −649 24 −3 10 26 22 6 12 −6 46 28 −4 9 26 23 6 13 −5 44 29 −4 9 26 23 6 14−4 42 30 −4 8 25 24 7 15 −4 39 33 −4 8 25 24 7 16 (half-pel) −4 36 36 −47 25 25 7 17 −4 33 39 −4 7 24 25 8 18 −4 30 42 −4 7 24 25 8 19 −4 29 44−5 6 23 26 9 20 −4 28 46 −6 6 23 26 9 21 −3 24 49 −6 6 22 26 10 22 −2 2052 −6 6 22 26 10 23 −2 18 53 −5 5 21 27 11 24 −2 16 54 −4 5 21 27 11 25−2 15 55 −4 5 20 27 12 26 −2 14 56 −4 4 20 28 12 27 −2 12 57 −3 4 19 2813 28 −2 10 58 −2 4 18 28 14 29 −1 7 60 −2 3 18 29 14 30 0 4 62 −2 3 1829 14 31 0 2 63 −1 3 17 29 15

Intra-predicted sample is calculated by convoluting with coefficientsselected from Table 2 according to subpixel offset and filter type asfollows:

${{s(x)} = \left( {{\sum\limits_{i = 0}^{i < 4}\left( {re{f_{i + x} \cdot c_{i}}} \right)} + 32} \right)}\operatorname{>>}6$

In this equation, “>>” indicates a bitwise shift-right operation.

Another set of interpolation filters that have 6-bit precision ispresented in Table 3.

TABLE 3 A set of interpolation filters with 6-bit precision ChromaDCT-IF Subpixel filter Gaussian filter offset c₀ c₁ c₂ c₃ c₀ c₁ c₂ c₃ 0(integer) 0 64 0 0 16 32 16 0 1 −1 63 2 0 15 29 17 3 2 −2 62 4 0 15 2917 3 3 −2 60 7 −1 14 29 18 3 4 −2 58 10 −2 13 29 18 4 5 −3 57 12 −2 1328 19 4 6 −4 56 14 −2 13 28 19 4 7 −4 55 15 −2 12 28 20 4 8 −4 54 16 −211 28 20 5 9 −5 53 18 −2 11 27 21 5 10 −6 52 20 −2 10 27 22 5 11 −6 4924 −3 9 27 22 6 12 −6 46 28 −4 9 26 23 6 13 −5 44 29 −4 9 26 23 6 14 −442 30 −4 8 25 24 7 15 −4 39 33 −4 8 25 24 7 16 (half-pel) −4 36 36 −4 824 24 8 17 −4 33 39 −4 7 24 25 8 18 −4 30 42 −4 7 24 25 8 19 −4 29 44 −56 23 26 9 20 −4 28 46 −6 6 23 26 9 21 −3 24 49 −6 6 22 27 9 22 −2 20 52−6 5 22 27 10 23 −2 18 53 −5 5 21 27 11 24 −2 16 54 −4 5 20 28 11 25 −215 55 −4 4 20 28 12 26 −2 14 56 −4 4 19 28 13 27 −2 12 57 −3 4 19 28 1328 −2 10 58 −2 4 18 29 13 29 −1 7 60 −2 3 18 29 14 30 0 4 62 −2 3 17 2915 31 0 2 63 −1 3 17 29 15

FIG. 11 illustrates a schematic diagram of a plurality of intraprediction modes used in the HEVC UIP scheme. For luminance blocks, theintra prediction modes may comprise up to 36 intra prediction modes,which may include three non-directional modes and 33 directional modes.The non-directional modes may comprise a planar prediction mode, a mean(DC) prediction mode, and a chroma from luma (LM) prediction mode. Theplanar prediction mode may perform predictions by assuming a blockamplitude surface with a horizontal and vertical slope derived from theboundary of the block. The DC prediction mode may perform predictions byassuming a flat block surface with a value matching the mean value ofthe block boundary. The LM prediction mode may perform predictions byassuming a chroma value for the block matches the luma value for theblock. The directional modes may perform predictions based on adjacentblocks as shown in FIG. 11.

H.264/AVC and HEVC specifies that a low-pass filter could be applied toreference samples prior being used in intra prediction process. Adecision on whether to use reference sample filter or not is determinedby intra prediction mode and block size. This mechanisms may be referredto as Mode Dependent Intra Smoothing (MDIS). There also exists aplurality of methods related to MDIS. For example, the AdaptiveReference Sample Smoothing (ARSS) method may explicitly (i.e. a flag isincluded into a bitstream) or implicitly (i.e., for example, data hidingis used to avoid putting a flag into a bitstream to reduce signalingoverhead) signal whether the prediction samples are filtered. In thiscase, the encoder may make the decision on smoothing by testing theRate-Distortion (RD) cost for all potential intra prediction modes.

In VVC, a partitioning mechanism based on both quad-tree and binary treeand known as QTBT is used. As depicted in FIG. 12, QTBT partitioning canprovide not just square but rectangular blocks as well. Of course, somesignaling overhead and increased computational complexity at the encoderside are the price of the QTBT partitioning as compared to conventionalquad-tree based partitioning used in the HEVC/H.265 standard.Nevertheless, the QTBT-based partitioning is endowed with bettersegmentation properties and, hence, demonstrates significantly highercoding efficiency than the conventional quad-tree.

Leaves of the trees used for partitioning are being processed in aZ-scan order, so that the current block corresponding to the currentleaf will have left and above neighbor blocks that are alreadyreconstructed during encoding or decoding processes, unless the currentblock is located on the boundary of the slice. This is also illustratedin FIG. 12. Left-to-right scan of the leaves of the tree shown in theright part of FIG. 12 corresponds to the spatial Z-scan order of theblocks shown in the right part of this figure. The same scan is appliedin case of quad-tree or multi-type trees.

For directional intra prediction, reference samples are obtained fromthe samples of the previously reconstructed neighboring blocks.Depending on the size of the block and intra prediction mode, a filtercould be applied to the reference samples prior they are used to obtainvalues of predicted samples.

In case of boundary smoothing and PDPC, several first columns or severalfirst rows of predicted block is combined with the additional predictionsignal generated from the neighboring samples.

When intra prediction is performed using horizontal intra predictionmode (for example, as illustrated in FIG. 10C as mode 18), referencesamples from the left side of the predicted block are column-wisereplicated, so that all samples within a row is set equal to thereference sample located on the this row at the left side of thepredicted block.

When intra prediction is performed using vertical intra prediction mode(for example, as illustrated in FIG. 10C as mode 50), reference samplesfrom the top side of the predicted block are row-wise replicated, sothat all samples within a column is set equal to the reference samplelocated on the this column at the top side of the predicted block.

In [A. Minezawa, K. Sugimoto, and S. Sekiguchi, “An improved intravertical and horizontal prediction,” contribution JCTVC-F172 to the 6thJCT-VC meeting, Torino, Italy, July 2011], the derivation process forvertical and horizontal intra prediction modes is specified as follows:

S′(x,y)=S(x,−1)+(S(−1,y)−S(−1,−1))/2^(x+1)   Vertical prediction:

S′(x,y)=S(−1,y)+(S(x,−1)−S(−1,−1))/2^(y+1)   Horizontal prediction:

where (x,y) indicates the position of prediction sample in a lumaprediction block as shown in FIG. 13A, S′(x, y) denotes predictedsamples and S(x, y) denotes the reference sample to be used forconventional prediction.

Since the value of S′(x, y) can fall out of the range of the minimump_(MIN) and the maximum p_(MAX) values of a predicted sample, a clippingfunction should be applied to, for example, as follows:

S′(x,y)=Clip3(p _(MIN) ,p _(MAX) ,S′(x,y)),

where Clip3( ) is a clipping function. Exemplary definition of thisfunction is given further.

For a predicted sample S(x, y) a nearest reference sample located abovethe predicted sample could be specified as S(x,−1). This nearestreference sample is located at the same column with the predictedsample.

Similarly, nearest reference sample located to the left of the predictedsample could be specified as S(−1, y). This nearest reference sample islocated at the same row with the predicted sample.

Particular implementation of simplified PDPC could be performeddifferently, depending on the intra prediction mode:

For planar, DC, HOR/VER intra prediction modes (denoted as 0, 1, 18, 50respectively in FIG. 10B and FIG. 10C), the following steps areperformed:

The predicted sample P (x, y) located at (x, y) is calculated asfollows:

P(x,y)=Clip1Cmp((wL×R _(−1,y) wT×R _(x,−1) −wTL×R_(−1,−1)+(64−wl−wT∓wTL)×P(x,y)+32))>>6)   (1)

where R_(x,−1), R_(−1,y) represent the reference samples located at topand left of the current sample (x, y), and R_(−1,−1) represents thetop-left sample, i.e. a reference sample located in the top-left cornerof the current block, the function clip1Cmp is set as follows:

-   -   If cIdx is equal to 0, clip1Cmp is set equal to Clip1Y,

Otherwise, clip 1Cmp  is  set  equal  to  Clip 1CClip 1_(Y)(x) = Clip 3(0, (1<< BitDepth_(Y)) − 1, x)Clip 1_(C)(x) = Clip 3(0, (1<< BitDepth_(C)) − 1, x)${{Clip}\; 3\left( {x,y,z} \right)} = \left\{ \begin{matrix}{x;} & {z < x} \\{y;} & {z > y} \\{{z;}\;} & {otherwise}\end{matrix} \right.$

BitDepth_(Y) is the bit depth of luma samples.

BitDepth_(C) is the bit depth of chroma samples.

BitDepth_(Y) and BitDepth_(C) could be signaled in sequence parameterset (SPS) of a bitstream.

Alternative definitions of Clip1Y(x) and Clip1C(x) are possible. Inparticular, as described by F. Galpin, P. Bordes, and F. Le Léannec incontribution WET-00040 “Adaptive Clipping in JEM2.0”,Clip1Cmp(x)=Clip3(min_(C), max_(C), x),

-   -   where min_(C) is the lower clipping bound used in current slice        for component ID C,    -   max_(C) is the upper clipping bound used in current slice for        component ID C,    -   C is a color component (e.g., Y for luma, Cb and Cr for chroma),    -   “x>>y” is an arithmetic right shift of a two's complement        integer representation of x by y binary digits. This function is        defined only for non-negative integer values of y. Bits shifted        into the most significant bits (MSBs) as a result of the right        shift have a value equal to the MSB of x prior to the shift        operation.

The DC mode weights are calculated as follows:

wT = 32>> ((y <  < 1)>> shift), wL = 32>> ((x <  < 1)>> shift), wTL = −(wL>> 4) − (wT>> 4), Where  shift = (log₂(width) + log₂(height) + 2)>> 2.

For planar mode, wTL=0, while for the horizontal mode wTL=wT and forvertical mode wTL=wL. DC mode PDPC weights (wL, wT, wTL) for (0, 0) and(1, 0) positions inside one 4×4 block are shown in FIG. 13B. From thisFigure it follows, that clipping operation in (1) is mandatory and thestate-of-the-art PDPC implementation has a potential flaw. The followingexample illustrates the case when the result could be out of the rangedetermined by BitDepth_(Y) or BitDepth_(C):

-   -   Given R_(−1,y)×0, R_(x,−1)=0, R_(−1,−1)=100, P(x,y)=0, from (1)        it follows that for (0,0) position of a 4×4 predicted block        P(x,y)=Clip1Cmp((wL×R_(−1,y)×wT×Rx_(x,−1)∓wTL×R_(−1,−1)+(64−wl−wT∓wTL)×P(x,y)+32))>>6)=Clip1Cmp((wTL×R_(−1,−1)+32)>>6)=Clip1Cmp((−4×100+32)>>6),    -   wTL==4 as shown in FIG. 13B.

As seen from the example above, a negative value “−4×100+32=−368” isbeing right-shifted using arithmetic bit shift. Depending on theimplementation, arithmetic right bit shift of negative value may lead todifferent output (e.g., in case of C/C++ programming language) and thusit could not be guaranteed that Clip 1Cmp output will always be 0, sincethe result of shifting a negative value to the right may have positivesign and non-zero magnitude in specific implementations.

For diagonal (denoted as 2 and 66 in FIG. 10B and FIG. 10C) and adjacentmodes (directional modes not less than 58 and not greater than 10 inFIG. 10B or FIG. 10C) processing is performed as described below usingthe same formula (1).

FIG. 14A illustrates the definition of reference samples R_(x,−1),R_(−1,y) and R_(−1,−1) for the extension of PDPC to the top-rightdiagonal mode. The prediction sample pred(x′, y′) is located at (x′, y′)within the prediction block. The coordinate x of the reference sampleR_(x,−1) is given by: x=x′+y′+1, and the coordinate y of the referencesample R_(−1,y) is similarly given by: y=x′+y′+1.

The PDPC weights for the top-right diagonal mode are:

-   -   wT=16>>((y′>>1)>>shift), wL=16>>((x′>>1)>>shift), wTL=0.

Similarly, FIG. 14B illustrates the definition of reference samplesR_(x,−1), R_(−1,y) and R_(−1,−1) for the extension of PDPC to thebottom-left diagonal mode. The coordinate x of the reference sampleR_(x,−1) is given by: x=x′+y′+1, and the coordinate y of the referencesample R_(−1,y) is: y=x′+y′+1. The PDPC weights for the top-rightdiagonal mode are: wT=16>>((y′<<1)>>shift), wL=16>>((x′<<1)>>shift),wTL=0. The case of an adjacent top-right diagonal mode is illustrated inFIG. 14C. The PDPC weights for an adjacent top-right diagonal mode are:wT=32>>((y′<<1)>>shift),wL=0, wTL=0. Similarly, the case of an adjacentbottom-left diagonal mode is illustrated in FIG. 14D. The PDPC weightsfor an adjacent bottom-left diagonal mode are: wL=32>>((x′<<1)>>shift),wT=0, wTL=0. The reference sample coordinates for the last two cases arecomputed using the tables that are already used for angular mode intraprediction. Linear interpolation of the reference samples is used iffractional reference sample coordinates are calculated.

Simplified PDPC could be performed as specified in the VVCspecification. Further the following denotation are used:

${{invAngle} = {{Round}\left( \frac{256*32}{intraPredAngle} \right)}},{{is}\mspace{14mu}{the}\mspace{14mu}{value}\mspace{14mu}{of}\mspace{14mu}{inverse}\mspace{14mu}{angle}},{{{Round}(x)} = {{{Sign}(x)}^{*}{{Floor}\left( {{{Abs}(x)} + {0{.5}}} \right)}}},{{{Sign}(x)} = \left\{ \begin{matrix}{1;} & {x > 0} \\{0;} & {x==0} \\{{- 1};} & {x < 0}\end{matrix} \right.}$

-   -   Floor(x) is the largest integer less than or equal to x,    -   Log 2(x) is the base-2 logarithm of x.    -   intraPredAngle is the angle parameter specified in Table 6,    -   A=C?B: D is a ternary assignment operation, where A is set equal        to B if condition C is true. Otherwise, if condition C is false,        A is set equal to D.    -   INTRA_PLANAR is a planar intra prediction mode ( )    -   INTRA_DC is a DC intra prediction mode,    -   INTRA_ANGULARXX is a one of directional intra prediction modes,        where XX denotes its number and corresponding direction shown in        FIG. 14B.        If a term is not explained herein, it is understood that its        definition can be found in the VVC specification or HEVC/H.265        standard specification.

Given the denotations above, the steps of simplified PDPC could bedefined as follows: Inputs to this process are:

-   -   the intra prediction mode predModeIntra,    -   a variable nTbW specifying the transform block width,    -   a variable nTbH specifying the transform block height,    -   a variable refW specifying the reference samples width,    -   a variable refH specifying the reference samples height,    -   the predicted samples predSamples[x][y], with x=0 . . . nTbW−1,        y=0 . . . nTbH−1,    -   the neighbouring samples p[x][y], with x=−1, y=−1 . . . refH−1        and x=0 . . . refW−1, y=−1,    -   a variable cIdx specifying the color component of the current        block.

Outputs of this process are the modified predicted samplespredSamples[x][y] with x=0 . . . nTbW−1, y=0 . . . nTbH−1.

Depending on the value of cIdx, the function clip1Cmp is set as follows:

-   -   If cIdx is equal to 0, clip1Cmp is set equal to Clip1_(Y).    -   Otherwise, clip1Cmp is set equal to Clip1_(C).        The variable nScale is set to ((Log 2(nTbW)+Log 2(nTbH)−2)>>2).        The reference sample arrays mainRef[x] and sideRef[y], with x=0        . . . refW−1 and y=0 . . . refH−1 are derived as follows:

mainRef[x]=p[x][−1]

sideRef[y]=p[−1 ][y]

The variables refL[x][y], ref[x][y], wT[y], wL[x] and wTL[x][y] with x=0. . . nTbW−1, y=0 . . . nTbH−1 are derived as follows:

-   -   If predModeIntra is equal to INTRA_PLANAR, INTRA_DC,        INTRA_ANGULAR18, or INTRA_ANGULAR50, the following applies:

refL[x][y]=p[−1][y]

refT[x][y]=p[x][−1]

wT[y]=32>>((y<<1)>>nScale)

wT[x]=32>>((x<<1)>>nScale)

wTL[x][y]=(predModelntra==INTRA_DC)?((wL[x]>>4)+(wT[y]>>4)):0

{x,y} define position of a predicted sample, wT, wL and wTL are weightsassociated with reference samples in accordance with the definedposition, nScale is a scaling parameter that controls propagationdistance (decay of weights wT and wL).

-   -   Otherwise, if predModeIntra is equal to INTRA_ANGULAR2 or        INTRA_ANGULAR66, the following applies:

refL[x][y]=p[−1][x+y1]

refT[x][y]=p[x+y+1][−1]

wT[y]=(32>>1)>>((y<<1)>>nScale)

wT[x]=(32>>1)>>((x<<1)>>nScale)

wTL[x][y]=0

-   -   Otherwise, if predModeIntra is less than or equal to        INTRA_ANGULAR10, the following ordered steps apply:        -   1. The variables dXPos[y], dXFrac[y], dXInt[y] and dX[x][y]            are derived as follows using invAngle:

dXPos[y]=((y+1)*invAngle+2)>>2

dXFrac[y]=dXPos[y]&63

dXInt[y]=dXPos[y]>>6

dX[x][y]=x+dXInt[y]

-   -    2. The variables refL[x][y], refT[x][y], wT[y], wL[x] and        wTL[x][y] are derived as follows:

refL[x][y]=0

refT[x][y]=(dX[x][y]<refW−1)?((64−dXFrac[x])*mainRef[dX[x][y]]+dXFrac[x]*mainRef[dX[x][y]+1]+32)>>6:0

wT[x]=(dX[x][y]<refW−1)?32>>((y<<1)>>nScale):0

wL[y]=0

wTL[x][y]=0   (eq. 1)

-   -   Otherwise, if predModeIntra is greater than or equal to        INTRA_ANGULAR58 (see FIG. 14B), the following ordered steps        apply:        -   1. The variables dYPos[x], dYFrac[x], dYInt[x] and dY[x][y]            are derived as follows using invAngle as specified in below            depending on intraPredMode:

dYPos[x]=((x+1)*invAngle+2)>>2

dYFrac[x]=dYPos[x]&63

dYInt[x]=dYPos[x]>>6

dY[x][y]=y+dYInt[x]

-   -    2. The variables refL[x][y], refT[x][y], wT[y], wL[x] and        wTL[x][y] are derived as follows:

refL[x][y]=(dY[x][y]<refH−1)?((64−dYFrac[x])*sideRef[dY[x][y]]+dYFrac[x]*sideRef[dY[x][y]+1]+32)>>6:0

refT[x][y]=0

wT[y]=0

wT[y]=0

wL[x]=(dY[x][y]<refH−1)?32>>((x<<1)>>nScale):0

wTL[x][y]=0   (eq. 2)

-   -   Otherwise, refL[x][y], refT[x][y], wT[y], wL[x] and wTL[x][y]        are all set equal to 0.        The values of the modified predicted samples predSamples[x][y],        with x=0 . . . nTbW−1, y=0 . . . nTbH−1 are derived as follows:

predSamples[x][y]=clip1Cmp((refL[x][y]*wL[x]+refT[x][y]*wT[y]−p[−1][−1]*wTL[x][y]+(64−wL[x]−wT[y]+wTL[x][y])*predSamples[x][y]+32)>>6);

In assignment Eq. 1 above simplified PDPC may use nearest-neighborinterpolation instead of linear one:

refT[][y]=(dX[x][y]<refW−1)?mainRef[dX[x][y]]: 0

Similarly, assignment Eq. 2 could also use nearest-neighborinterpolation:

refL[][y]=(dY[x][y]<refL−1)?sideRef[dY[x][y]]: 0

Clipping may be removed just for several modes. Specifically for the DCintra prediction mode, wTL may be set to zero. Consequently, clip 1 Cmp() operation will not be required for PDPC if intra prediction mode isDC. The following rules or methods may be applied:

-   -   pdpc for DC does not use top-left (TL) sample;    -   clipping operation in PDPC is not performed for any intra        prediction mode except for HOR and VER modes;    -   PDPC for HOR and VER mode uses clipping operation and do not use        thresholding described in this application.

According to the description above, the specification could be modifiedin the following way:

-   -   If predModeIntra is equal to INTRA_PLANAR or INTRA_DC, the        following applies:

refL[x][y]=p[−1][y]  (8-227)

refT[x][y]=p[x][−1]  (8-228)

wT[y]=32>>((y<<1)>>nScale)   (8-229)

wL[x]=32>>((x<<1)>>nScale)   (8-230)

wTL[x][y]=0   (8-231)

-   -   Otherwise, if predModeIntra is equal to INTRA_ANGULAR18 or        INTRA_ANGULAR50, the following applies:

refL[x][y]=p[−1][y]  (8-232)

refT[x][y]=p[x][−1]  (8-233)

wT[y]=(predModeIntra==INTRA_ANGULAR18)?32>>((y<<1)>>nScale):0   (8-234)

wL[x]=(predModeIntra==INTRA_ANGULAR50)?32>>((x<<1)>>nScale):0   (8-236)

wTL[x][y]=(predModelntra==INTRA_ANGULAR18)?wT[y]:wL[x]  (8-236)

-   -   Otherwise, if predModeIntra is equal to INTRA_ANGULAR2 or        INTRA_ANGULAR66, the following applies:

refL[x][y]=p[−1][x+y1]  (8-237)

refT[x][y]=p[x+y+1][−1]  (8-238)

wT[y]=(32>>1)>>((y<<1)>>nScale)   (8-239)

wL[x]=(32>>1)>>((x<<1)>>nScale)   (8-240)

wTL[x][y]=0   (8-241)

-   -   Otherwise, if predModeIntra is less than or equal to        INTRA_ANGULAR10, the following steps apply:

-   1. The variables dXPos[y], dXFrac[y], dXInt[y] and dX[x][y] are    derived as follows using invAngle as specified in VVC specification    draft depending on intraPredMode:

dXPos[y]=((y+1)*invAngle+2)>>2

dXFrac[y]=dXPos[y]&63

dXInt[y]=dXPos[y]>>6

dX[x][y]=x+dXInt[y]  (8-242)

-   2. The variables refL[x][y], refT[x][y], wT[y], wL[x] and wTL[x][y]    are derived as follows:

refL[x][y]=0   (8-243)

refT[x][y]=(dX[x][y]<refW−1)?mainRef[dX[x][y]+dXFrac[y]>>5)]:0   (8-244)

wT[y]=(dX[x][y]<refW−1)?32>>((y<<1)>>nScale):0   (8-245)

wL[x]=0   (8-246)

wTL[x][y]=0   (8-247)

-   -   Otherwise, if predModeIntra is greater than or equal to        INTRA_ANGULAR58, the following ordered steps apply:

-   1. The variables dYPos[x], dYFrac[x], dYInt[x] and dY[x][y] are    derived as follows using invAngle as specified in VVC specification    draft depending on intraPredMode:

dYPos[x]=((x+1)*invAngle+2)>>2

dYFrac[x]=dYPos[y]&63

dYInt[x]=dYPos[y]>>6

dY[x][y]=y+dYInt[x]  (8-248)

-   2. The variables refL[x][y], refT[x][y], wT[y], wL[x] and wTL[x][y]    are derived as follows:

refL[x][y]=(dY[x][y]<refH−1)?sideRef[dY[x][y]+dYFrac[x]>>5)]:0   (8-249)

refT[x][y]=0   (8-250)

wT[y]=0   (8-251)

wL[x]=(dY[x][y]<refH−1)?32>>((x<<1)>>nScale):0   (8-252)

wTL[x][y]=0   (8-253)

-   -   Otherwise, refL[x][y], refT[x][y], wT[y], wL[x] and wTL[x][y]        are all set equal to 0.        The values of the modified predicted samples predSamples[x][y],        with x=0 . . . nTbW−1, y=0 . . . nTbH−1 are derived as follows:    -   If predModeIntra is equal to INTRA_ANGULAR18 or INTRA_ANGULAR50:

predSamples[x][y]=clip1Cmp((refL[x][y]*wL[x]+refT[x][y]*wT[y]−p[−1][−1]*wTL[x][y]+(64−wL[x]−wT[y]+wTL[x][y])*predSamples[x][y]+32)>>6)  (1*)

-   -   Otherwise, the following applies:

predSamples[x][y]=refL[x][y]*wL[x]+refT[x][y]*wT[y](64−wL[x]−wT[y]predSamples[x][y]+32)>>6

According to the text of specification above, the followingmodifications were introduced to the PDPC method:

-   -   when performing PDPC for DC, top-left sample is not considered;    -   clipping is applied to the PDPC output value of predicted        samples only for horizontal and vertical the intra prediction        modes. For all the other intra prediction modes clipping is not        performed.

At both encoder and decoder sides, proposed method uses the following asthe input data:

-   -   directional intra prediction mode (denoted further as        predModeIntra, which is shown in FIG. 10B and FIG. 10C),    -   block size parameter nTbS, which is set equal to (log        2(nTbW)+Log 2(nTbH))>>1, where nTbW and nTbH denote width and        height of the predicted block, respectively, and “>>” denotes a        right-shift operation.

The modification of the VVC specification that enables usage of theproposed method may comprise substituting “the neighbouring samplesp[x][y]” by “the reference samples p[x][y]” in the section describingsimplified PDPC.

The angle parameter intraPredAngle denotes the subpixel offset betweentwo adjacent rows of predicted samples in fixed point representationhaving length of fractional part equal to 5-bits. This parameter couldbe derived from the intra prediction mode is derived from predModeIntraand. An exemplary derivation of intraPredAngle from predModeIntra couldbe defined with a LUT, e.g., as it is shown in Table 6.

TABLE 6 An exemplary LUT to derive intraPredAngle from predModeIntra.predModeIntra −14 −13 −12 −11 intraPredAngle 512 341 256 171predModeIntra −10 −9 −8 −7 −6 −5 −4 −3 −2 −1 2 3 4 5 6 7 8intraPredAngle 128 102 86 73 64 57 51 45 39 35 32 29 26 23 20 18 16predModeIntra 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25intraPredAngle 14 12 10 8 6 4 3 2 1 0 −1 −2 −3 −4 −6 −8 −10predModeIntra 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42intraPredAngle −12 −14 −16 −18 −20 −23 −26 −29 −32 −29 −26 −23 −20 −18−16 −14 −12 predModeIntra 43 44 45 46 47 48 49 50 51 52 53 54 55 56 5758 59 intraPredAngle −10 −8 −6 −4 −3 −2 −1 0 1 2 3 4 6 8 10 12 14predModeIntra 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76intraPredAngle 16 18 20 23 26 29 32 35 39 45 51 57 64 73 86 102 128predModeIntra 77 78 79 80 intraPredAngle 171 256 341 512

From the current HEVC and VVC draft specification, planar intraprediction method is used. The part of the VVC draft 3 is incorporatedbelow for reference:

8.2.4.2.5. Specification of INTRA_PLANAR intra prediction modeInputs to this process are:

-   -   a variable nTbW specifying the transform block width,    -   a variable nTbH specifying the transform block height,    -   the neighbouring samples p[x][y], with x=−1, y=−1 . . . nTbH and        x=0 . . . nTbW, y=−1.        Outputs of this process are the predicted samples        predSamples[x][y], with x=0 . . . nTbW−1, y=0 . . . nTbH−1        The values of the prediction samples predSamples[x][y], with x=0        . . . nTbW−1 and y=0 . . . nTbH−1, are derived as follows:

predV[x][y]=((nTbH−1−y)*p[x][−1]+(y+1)*p[−1][nTbH])<<Log 2(nTbW)  (8-82)

predH[x][y]=((nTbW−1−x)*p[y][−1]+(x+1)*p[nTbW][−1])<<Log 2(nTbH)  (8-83)

predSamples[x][y]=(predV[x][y]predH[x][y]+nTbW*nTbH)>>(Log 2(nTbW)+Log2(nTbH)+1)   (8-84)

The proposed solution is an alternative PDPC method that does not havethe flaw of equation (1*). Specifically, the method may comprise thefollowing steps:

The predicted sample P(x, y) located at (x, y) is calculated as follows:

P(x,y)=(wL×R _(−1,y) +wT×R _(x, −1)+(64−wL−wT)×P(x,y)+32))>>>>6   (2)

where R_(x,−1), R_(−1,y) represents the reference samples located aboveand to the left of the current sample (x, y). It is worth noting thatthe function clip1Cmp is not in use in equation (2) since the values ofthe predicted sample P(x, y) are always in the range of valid values,i.e. between minimum and maximum of pixel values.

“x>>y” is an arithmetic right shift of a two's complement integerrepresentation of x by y binary digits. This function is defined onlyfor non-negative integer values of y. Bits shifted into the mostsignificant bits (MSBs) as a result of the right shift have a valueequal to the MSB of x prior to the shift operation.

The DC mode weights are calculated as follows:

wT=32>>((y<<1)>>shift),wL=32>>((x<<1)>>shift),

DC mode PDPC weights (wL, wT) for (0, 0) and (1, 0) positions inside one4×4 block are shown in FIG. 15. It could be noticed, that in comparisonwith FIG. 13B, top-left reference sample is not used and weight for thissample is not specified.

This alternative method could be represented in the form of a part ofVVC specification:

Position-dependent intra prediction sample filtering processInputs to this process are:

-   -   the intra prediction mode predModeIntra,    -   a variable nTbW specifying the transform block width,    -   a variable nTbH specifying the transform block height,    -   a variable refW specifying the reference samples width,    -   a variable refH specifying the reference samples height,    -   the predicted samples predSamples[x][y], with x=0 . . . nTbW−1,        y=0 . . . nTbH−1,    -   the neighbouring samples p[x][y], with    -   x=−1, y=−1 . . . refH−1 and x=0 . . . refW−1, y=−1,    -   a variable cIdx specifying the colour component of the current        block.        Outputs of this process are the modified predicted samples        predSamples[x][y] with x=0 . . . nTbW−1, y=0 . . . nTbH−1.        Depending on the value of cIdx, the function clip1Cmp is set as        follows:    -   If cIdx is equal to 0, clip1Cmp is set equal to Clip1_(Y).    -   Otherwise, clip1Cmp is set equal to Clip1_(C).        The variable nScale is set to ((Log 2(nTbW)+Log 2(nTbH)−2)>>2).        The reference sample arrays mainRef[x] and sideRef[y], with x=0        . . . refW−1 and y=0 . . . refH−1 are derived as follows:

mainRef[x]=p[x][−1]

sideRef[y]=p[−1 ][y]

The variables refL[x][y], refT[if x][y], wT[y] and wL[x] with x=0 . . .nTbW−1, y=0 . . . nTbH−1 are derived as follows:

-   -   If predModeIntra is equal to INTRA_PLANAR, INTRA_DC,        INTRA_ANGULAR18, or INTRA_ANGULAR50, the following applies:

refL[x][y]=p[−1][y]

refT[x][y]=p[x][−1]

wT[y]=32>>((y<<1)>>nScale)

wL[x]=32>>((x<<1)>>nScale)

-   -   Otherwise, if predModeIntra is equal to INTRA_ANGULAR2 or        INTRA_ANGULAR66, the following applies:

refL[x][y]=p[−1][x+y1]

refT[x][y]=p[x+y+1][−1]

wT[y]=(32>>1)>>((y<<1)>>nScale)

wL[x]=(32>>1)>>((x<<1)>>nScale)

-   -   Otherwise, if predModeIntra is less than or equal to        INTRA_ANGULAR10, the following ordered steps apply:    -   1. The variables dXPos[y], dXFrac[y], dXInt[y] and dX[x][y] are        derived as follows using invAngle depending on intraPredMode:

dXPos[y]=((y+1)*invAngle+2)>>2

dXFrac[y]=dXPos[y]&63

dXInt[y]=dXPos[x]>>6

dX[x][y]=x+dXInt[x]

-   -    invAngle may be specified in VVC specification draft.    -   2. The variables refL[x][y], refT[x][y], wT[y], wL[x] are        derived as follows:

refL[x][y]=0

refT[x][y]=(dX[x][y]<refW−1)?((64−dXFrac[x])*mainRef[dX[x][y]]+dXFrac[y]*mainRef[dX[x][y]1]+32)>>6:0

wT[y]=(dX[x][y]<refW−1)?32>>((y<<1)>>nScale):0

wL[x]=0

-   -   Otherwise, if predModeIntra is greater than or equal to        INTRA_ANGULAR58, the following ordered steps apply:    -   1. The variables dYPos[x], dYFrac[x], dYInt[x] and dY[x][y] are        derived as follows using invAngle depending on intraPredMode:

dYPos[x]=((x+1)*invAngle+2)>>2

dYFrac[x]=dYPos[x]&63

dYInt[x]=dYPos[x]>>6

dY[x][y]=y+dYInt[x]

-   -    invAngle may be specified in VVC specification draft.    -   2. The variables refL[x][y], refT[x][y], wT[y] and wL[x] are        derived as follows:

refL[x][y]=(dY[x][y]<refH−1)?((64−dYFrac[x])*sideRef[dY[x][y]]+dYFrac[y]*sideRef[dY[x][y]+1]+32)>>6:0

refT[x][y]=0

wT[y]=0

wL[x]=(dY[x][y]<refH−1)?32>>((x<<1)>>nScale):0

-   -   Otherwise, refL[x][y], refT[x][y], wT[y], wL[x] are all set        equal to 0. The values of the modified predicted samples        predSamples[x][y], with x=0 . . . nTbW−1, y=0 . . . nTbH−1 are        derived as follows:

predSamples[x][y]=(refL[x][y]*wL[x]+refT[x][y]*wT[y]+(64−wL[x]−wT[y])*predSamples[x][y]+32)>>6)

-   -   Here “(64−wL[x]−wT[y])” stands for sample weighting factor.

FIG. 16 illustrates the above-described method. By dashed line the stepof clipping is shown, that is performed in the state-of-the-art PDPC,but is not performed in the proposed method, since it is not required,because the only negative coefficient wTL is not used.

In FIG. 17, reference samples are used by the intra prediction processto produce predicted samples. Each predicted sample is further weightedusing a sample weighting factor. The sample weighting factor may, forexample, be equal to (64−wL[x]−wT[y]). The same reference samples areused to calculate additional values for each of the predicted samplesdepending on x and y, where x and y define the position of a predictedsample within a predicted block. These additional values are added tocorresponding weighted predicted samples. Each sample resulting fromthis operation is then normalized by right-shifting it according to thepredetermined precision of the sample weighting factor. For example, ifthe sample weighting factor is defined as (64−wL[x]−wT[y])) theprecision is 6 bits. Therefore at this step a right-shift by 6 isperformed in order to ensure that possible minimum and maximum values ofthe output values are the same as the possible minimum and maximumvalues of the reference samples.

One of the beneficial effects of the proposed solution is that thePLANAR intra prediction mechanism can be reused to calculate theadditional values. Specifically, PLANAR intra prediction uses thefollowing equation to derive horizontal and vertical predicted samplevalues:

predV[x][y]=((nTbH−1−−y)*p[x][−1]++(y+1)*p[−1][nTbH])<<Log 2(nTbW)  (8-82)

predH[x][y]=((nTbW−1−−x)*p[−1][y]++(x+1)*p[nTbW][−1])<<Log 2(nTbH)  (8-83)

From the two above equations it can be seen that predV[x][y] usesreference sample p[x][−1] located in the same column as predV[x][y] doesand predH[x][y] uses the reference sample p[−1][y] located on the samerow with predH[x][y]. Besides, left-shift operations are performed asthe final step and thus can be skipped since they do not affectintermediate calculations that are being reused. nTbW, nTbH, x and yvariables are inputs of PLANAR intra prediction method and thus could beadjusted correspondingly. Because of that it is possible to substitute(nTbW−1−x) by D_(x) and (nTbH−1−y) by D_(y) input variables. Bottom-leftand top-right reference samples could be set to 0 since these are not aparameter being used.

Considering the above-described observations, equations above may berewritten in accordance with its inputs being predetermined:

V _(y) =Dy*p[x][−1]

V _(x) =Dx*p[−1][y]

Thus, the following unifications could be performed:

-   -   an additional value in case of horizontal mode (mode 18) could        be calculated as V_(y)=Dy*p[x][−1], wherein D_(y) is set equal        to wT[y];    -   an additional value in case of vertical mode (mode 50) could be        calculated as V_(x)=Dx*p[−1][y], wherein D_(x) is set equal to        wL[y];    -   an additional value in case of DC mode (mode 1) could be        calculated as V_(y)+V_(x), wherein D_(x) and D_(y) are set as in        the previous two cases.

By alternation of reference sample selection, it could be shown thatunification could be performed for all the intra prediction modes thatare specified for PDPC process.

When intra prediction mode is specified to be equal to DC, horizontal orvertical intra prediction modes, the resulting updated predicted sampleshould be clipped, e.g. as it is shown in FIG. 16 by a block with dashedborder.

In case of horizontal or vertical intra prediction modes it is morebeneficial to reposition the clipping operation before the last step ofsimplified PDPC when weighted predicted sample is being summed with anadditional value. This additional value is obtained differently fordifferent modes as described above.

Embodiments of the invention propose to threshold results ofintermediate calculations that are performed to obtain the additionalvalue for the cases of vertical or horizontal intra prediction modes areused in intra prediction. For these cases an additional value could becalculated in such a way that being added to the weighted predictedsample it will not require clipping operation.

The state-of-the-art PDPC methods applies clipping on the updatedpredicted sample (even for horizontal and vertical modes). Specifically:

predSamples[x][y]=clip1Cmp((refL[x][y]*wL[x]+refT[x][y]*wT[y]−p[−1][−1]*wTL[x][y]+(64−wL[x]−wT[y]+wTL[x][y])*predSamples[x][y]+32)>>6);

For horizontal intra prediction mode wTL[x][y] is set equal to wT[y]thus leading to the simplified expression:

predSamples[x][y]=clip1Cmp(refT[x][y]−p[−1][−1]*wT[y]+64*predSamples[x][y]+32)>>6;)

In this expression, “refT[x][y]−p[−1][−1]” is in fact the additionalreference sample value. I.e., for the cases when the intra predictionmode is horizontal, additional reference sample value is set equal tothe difference between the value of the nearest reference sample(refT[x][y]) located above the predicted sample and the value of thetop-left reference sample (p[−1][−1]).

For the cases when intra prediction mode is vertical, additionalreference sample value is set equal to the difference between the valueof the nearest reference sample (refL[x][y]) located to the left of thepredicted sample and the value of the top-left reference sample(p[−1][−1]), i.e. to “refL[x][y]−p[−1][−1]”.

Hence, it is possible to replace clipCmp function by thresholdingoperations over the additional reference sample value, i.e.“refT[x][y]−p[−1][−1]”.

For a horizontal intra prediction mode:

predSamples[x][y]=(T(refT[x][y]−p[−1][−1])*wT[y]+64*predSamples[x][y]+32)>>6,

where T( ) is a thresholding operation.

For a vertical intra prediction mode:

predSamples[x][y]=(T(refL[x][y]−p[−1][−1])*wT[y]+64*predSamples[x][y]+32)>>6,

where T( ) is a thresholding operation.

Exemplary implementation of T( ) is given in FIG. 17. Thresholdingoperation T( ) of additional reference sample value is in fact updatingthe additional reference sample value in accordance with whethertop-left reference sample value is greater than predicted sample value.In specific:

-   -   when the top-left reference sample value is greater than the        predicted sample value, the lower limit is obtained by        subtracting predicted sample value from the maximum value of the        predicted sample, the updated additional reference sample value        is set equal to the maximum of two values,        -   the first value is the additional reference sample value,            and        -   the second value is the lower limit,    -   otherwise, the upper limit is obtained by subtracting predicted        sample value from the minimum value of the predicted sample, the        updated additional reference sample value is set equal to the        minimum of two values,        -   the first value is the additional reference sample value,            and        -   the second value is the upper limit.

In FIG. 17, the closest reference sample is a nearest reference samplelocated to the left of the predicted sample when intra prediction ishorizontal. When intra prediction is vertical, the closest referencesample is a nearest reference sample located above the predicted sample.From this figure it could be noticed that comparison result is used toswitch both:

-   -   results of thresholding functions, i.e. minimum and maximum, and    -   one of the arguments of the thresholding function.

It is noteworthy that Clip3( ) function provides two thresholdingoperations. One threshold is the minimum value of the predicted sampleand the other one is the maximum value of the predicted sample. Incomparison with Clip3( ) function applied to the updated predictedsample (FIG. 16), the proposed thresholding (FIG. 17) applies only onethreshold: either the minimum value of the predicted sample or themaximum value of the predicted sample.

It could also be noticed that the above-described thresholdingreposition enables usage of the same equation without clipping for allof the intra predicted modes, where PDPC is applicable.

FIG. 18 is a block diagram showing an example structure of an apparatus1800 for intra predicting a block of a picture. The apparatus 1800 isconfigured to carry out the above methods, and may include:

an obtaining unit 1810, configured to obtain a predicted sample valuefrom one or more reference sample values by intra-prediction using anintra prediction mode, obtain at least one additional reference samplevalue in accordance with the intra prediction mode, and obtain athresholded additional reference sample value based on the additionalreference sample value;

a calculating unit 1820, configured to calculate an additional valuefrom the thresholded additional reference sample value, multiply thepredicted sample value by a sample weighting factor, resulting in aweighted predicted sample value, add the additional value to theweighted predicted sample value, resulting in a non-normalized predictedsample value, and normalize the non-normalized predicted sample value,resulting in a normalized predicted sample value.

When intra prediction mode is vertical intra prediction mode, theadditional reference sample value may be set equal to the differencebetween the value of the nearest reference sample located above thepredicted sample and the value of the top-left reference sample.

When the intra prediction mode is horizontal intra prediction mode, theadditional reference sample value may be set equal to the differencebetween the value of the nearest reference sample located to the left ofthe predicted sample and the value of the top-left reference sample.

When the intra prediction mode is DC intra prediction mode, the at leastone additional reference sample value include a first additionalreference sample value and a second additional reference sample value,and the first additional reference sample value and the secondadditional reference sample value may be obtained by:

-   -   setting the first additional reference sample value equal to the        value of the nearest reference sample located to the left of the        predicted sample, and    -   setting the second additional reference sample value equal to        the value of the nearest reference sample located to the above        of the predicted sample.

When a top-left reference sample value is greater than or equal to thepredicted sample value, an upper limit is obtained by subtractingpredicted sample value from the maximum value of the predicted sample,the thresholded additional reference sample value is set equal to themaximum of a first value and a second value:

-   -   the first value is the additional reference sample value, and    -   the second value is the upper limit.

When a top-left reference sample value is less than the predicted samplevalue, a lower limit is obtained by subtracting predicted sample valuefrom the minimum value of the predicted sample, the thresholdedadditional reference sample value is set equal to the minimum of a firstvalue and a second value:

-   -   the first value is the additional reference sample value, and    -   the second value is the lower limit.

Following is an explanation of the applications of the encoding methodas well as the decoding method as shown in the above-mentionedembodiments, and a system using them.

FIG. 19 is a block diagram showing a content supply system 3100 forrealizing content distribution service. This content supply system 3100includes capture device 3102, terminal device 3106, and optionallyincludes display 3126. The capture device 3102 communicates with theterminal device 3106 over communication link 3104. The communicationlink may include the communication channel 13 described above. Thecommunication link 3104 includes but not limited to WIFI, Ethernet,Cable, wireless (3G/4G/5G), USB, or any kind of combination thereof, orthe like.

The capture device 3102 generates data, and may encode the data by theencoding method as shown in the above embodiments. Alternatively, thecapture device 3102 may distribute the data to a streaming server (notshown in the Figures), and the server encodes the data and transmits theencoded data to the terminal device 3106. The capture device 3102includes but not limited to camera, smart phone or Pad, computer orlaptop, video conference system, PDA, vehicle mounted device, or acombination of any of them, or the like. For example, the capture device3102 may include the source device 12 as described above. When the dataincludes video, the video encoder 20 included in the capture device 3102may actually perform video encoding processing. When the data includesaudio (i.e., voice), an audio encoder included in the capture device3102 may actually perform audio encoding processing. For some practicalscenarios, the capture device 3102 distributes the encoded video andaudio data by multiplexing them together. For other practical scenarios,for example in the video conference system, the encoded audio data andthe encoded video data are not multiplexed. Capture device 3102distributes the encoded audio data and the encoded video data to theterminal device 3106 separately.

In the content supply system 3100, the terminal device 310 receives andreproduces the encoded data. The terminal device 3106 could be a devicewith data receiving and recovering capability, such as smart phone orPad 3108, computer or laptop 3110, network video recorder (NVR)/digitalvideo recorder (DVR) 3112, TV 3114, set top box (STB) 3116, videoconference system 3118, video surveillance system 3120, personal digitalassistant (PDA) 3122, vehicle mounted device 3124, or a combination ofany of them, or the like capable of decoding the above-mentioned encodeddata. For example, the terminal device 3106 may include the destinationdevice 14 as described above. When the encoded data includes video, thevideo decoder 30 included in the terminal device is prioritized toperform video decoding. When the encoded data includes audio, an audiodecoder included in the terminal device is prioritized to perform audiodecoding processing.

For a terminal device with its display, for example, smart phone or Pad3108, computer or laptop 3110, network video recorder (NVR)/digitalvideo recorder (DVR) 3112, TV 3114, personal digital assistant (PDA)3122, or vehicle mounted device 3124, the terminal device can feed thedecoded data to its display. For a terminal device equipped with nodisplay, for example, STB 3116, video conference system 3118, or videosurveillance system 3120, an external display 3126 is contacted thereinto receive and show the decoded data.

When each device in this system performs encoding or decoding, thepicture encoding device or the picture decoding device, as shown in theabove-mentioned embodiments, can be used.

FIG. 20 is a diagram showing a structure of an example of the terminaldevice 3106. After the terminal device 3106 receives stream from thecapture device 3102, the protocol proceeding unit 3202 analyzes thetransmission protocol of the stream. The protocol includes but notlimited to Real Time Streaming Protocol (RTSP), Hyper Text TransferProtocol (HTTP), HTTP Live streaming protocol (HLS), MPEG-DASH,Real-time Transport protocol (RTP), Real Time Messaging Protocol (RTMP),or any kind of combination thereof, or the like.

After the protocol proceeding unit 3202 processes the stream, streamfile is generated. The file is outputted to a demultiplexing unit 3204.The demultiplexing unit 3204 can separate the multiplexed data into theencoded audio data and the encoded video data. As described above, forsome practical scenarios, for example in the video conference system,the encoded audio data and the encoded video data are not multiplexed.In this situation, the encoded data is transmitted to video decoder 3206and audio decoder 3208 without through the demultiplexing unit 3204.

Via the demultiplexing processing, video elementary stream (ES), audioES, and optionally subtitle are generated. The video decoder 3206, whichincludes the video decoder 30 as explained in the above mentionedembodiments, decodes the video ES by the decoding method as shown in theabove-mentioned embodiments to generate video frame, and feeds this datato the synchronous unit 3212. The audio decoder 3208, decodes the audioES to generate audio frame, and feeds this data to the synchronous unit3212. Alternatively, the video frame may store in a buffer (not shown inFIG. Y) before feeding it to the synchronous unit 3212. Similarly, theaudio frame may store in a buffer (not shown in FIG. Y) before feedingit to the synchronous unit 3212.

The synchronous unit 3212 synchronizes the video frame and the audioframe, and supplies the video/audio to a video/audio display 3214. Forexample, the synchronous unit 3212 synchronizes the presentation of thevideo and audio information. Information may code in the syntax usingtime stamps concerning the presentation of coded audio and visual dataand time stamps concerning the delivery of the data stream itself.

If subtitle is included in the stream, the subtitle decoder 3210 decodesthe subtitle, and synchronizes it with the video frame and the audioframe, and supplies the video/audio/subtitle to a video/audio/subtitledisplay 3216.

Embodiments of the present invention are not limited to theabove-mentioned system, and either the picture encoding device or thepicture decoding device in the above-mentioned embodiments can beincorporated into other system, for example, a car system.

Although embodiments of the invention have been primarily describedbased on video coding, it should be noted that embodiments of the codingsystem 10, encoder 20 and decoder 30 (and correspondingly the system 10)and the other embodiments described herein may also be configured forstill picture processing or coding, i.e. the processing or coding of anindividual picture independent of any preceding or consecutive pictureas in video coding. In general only inter-prediction units 244 (encoder)and 344 (decoder) may not be available in case the picture processingcoding is limited to a single picture 17. All other functionalities(also referred to as tools or technologies) of the video encoder 20 andvideo decoder 30 may equally be used for still picture processing, e.g.residual calculation 204/304, transform 206, quantization 208, inversequantization 210/310, (inverse) transform 212/312, partitioning 262/362,intra-prediction 254/354, and/or loop filtering 220, 320, and entropycoding 270 and entropy decoding 304.

Although embodiments of the invention have been primarily describedbased on video coding, it should be noted that embodiments of the codingsystem 10, encoder 20 and decoder 30 (and correspondingly the system 10)and the other embodiments described herein may also be configured forstill picture processing or coding, i.e. the processing or coding of anindividual picture independent of any preceding or consecutive pictureas in video coding. In general only inter-prediction units 244 (encoder)and 344 (decoder) may not be available in case the picture processingcoding is limited to a single picture 17. All other functionalities(also referred to as tools or technologies) of the video encoder 20 andvideo decoder 30 may equally be used for still picture processing, e.g.,residual calculation 204/304, transform 206, quantization 208, inversequantization 210/310, (inverse) transform 212/312, partitioning 262/362,intra-prediction 254/354, and/or loop filtering 220, 320, and entropycoding 270 and entropy decoding 304.

Embodiments, e.g., of the encoder 20 and the decoder 30, and functionsdescribed herein, e.g., with reference to the encoder 20 and the decoder30, may be implemented in hardware, software, firmware, or anycombination thereof. If implemented in software, the functions may bestored on a computer-readable medium or transmitted over communicationmedia as one or more instructions or code and executed by ahardware-based processing unit. Computer-readable media may includecomputer-readable storage media, which corresponds to a tangible mediumsuch as data storage media, or communication media including any mediumthat facilitates transfer of a computer program from one place toanother, e.g., according to a communication protocol. In this manner,computer-readable media generally may correspond to (1) tangiblecomputer-readable storage media which is non-transitory or (2) acommunication medium such as a signal or carrier wave. Data storagemedia may be any available media that can be accessed by one or morecomputers or one or more processors to retrieve instructions, codeand/or data structures for implementation of the techniques described inthis disclosure. A computer program product may include acomputer-readable medium.

By way of example, and not limiting, such computer-readable storagemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage, or other magnetic storage devices, flashmemory, or any other medium that can be used to store desired programcode in the form of instructions or data structures and that can beaccessed by a computer. Also, any connection is properly termed acomputer-readable medium. For example, if instructions are transmittedfrom a website, server, or other remote source using a coaxial cable,fiber optic cable, twisted pair, digital subscriber line (DSL), orwireless technologies such as infrared, radio, and microwave, then thecoaxial cable, fiber optic cable, twisted pair, DSL, or wirelesstechnologies such as infrared, radio, and microwave are included in thedefinition of medium. It should be understood, however, thatcomputer-readable storage media and data storage media do not includeconnections, carrier waves, signals, or other transitory media, but areinstead directed to non-transitory, tangible storage media. Disk anddisc, as used herein, includes compact disc (CD), laser disc, opticaldisc, digital versatile disc (DVD), floppy disk and Blu-ray disc, wheredisks usually reproduce data magnetically, while discs reproduce dataoptically with lasers. Combinations of the above should also be includedwithin the scope of computer-readable media.

Instructions may be executed by one or more processors, such as one ormore digital signal processors (DSPs), general purpose microprocessors,application specific integrated circuits (ASICs), field programmablelogic arrays (FPGAs), or other equivalent integrated or discrete logiccircuitry. Accordingly, the term “processor,” as used herein may referto any of the foregoing structure or any other structure suitable forimplementation of the techniques described herein. In addition, in someaspects, the functionality described herein may be provided withindedicated hardware and/or software modules configured for encoding anddecoding, or incorporated in a combined codec. Also, the techniquescould be fully implemented in one or more circuits or logic elements.The processing circuitry mentioned in this disclosure may comprisehardware and software.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components,modules, or units are described in this disclosure to emphasizefunctional aspects of devices configured to perform the disclosedtechniques, but do not necessarily require realization by differenthardware units. Rather, as described above, various units may becombined in a codec hardware unit or provided by a collection ofinteroperative hardware units, including one or more processors asdescribed above, in conjunction with suitable software and/or firmware.

1. A method of intra predicting a block of a picture, comprising:obtaining an intra prediction mode of a current block; and performing aclipping operation in position-dependent prediction combination (PDPC)when the intra prediction mode is a horizontal intra prediction mode ora vertical intra prediction mode, wherein the clipping operation is notperformed when the intra prediction mode is DC mode or planar mode. 2.The method of claim 1, wherein the clipping operation in PDPC isperformed only when the intra prediction mode is the horizontal intraprediction mode or the vertical intra prediction mode.
 3. The method ofclaim 1, wherein when predModeIntra is equal to INTRA_ANGULAR18 orINTRA_ANGULAR50, the method comprises applying:predSamples[x][y]=clip1Cmp((refL[x][y]*wL[x]+refT[x][y]*wT[y]−p[−1][−1]*wTL[x][y]+(64−wL[x]−wT[y]+wTL[x][y])*predSamples[x][y]+32)>>6);and wherein predModeIntra indicates the intra prediction mode, {x,y}define position of a predicted sample, and wT, wL and wTL are weightsassociated with reference samples in accordance with a defined position.4. The method of claim 1, wherein when predModeIntra is not equal toINTRA_ANGULAR18 or INTRA_ANGULAR50, the method comprises applying:predSamples[x][y]=(refL[x][y]*wL[x]+refT[x][y]*wT[y](64−wL[x]−wT[y])*predSamples[x][y]+32)>>6;and wherein predModeIntra indicates the intra prediction mode, {x,y}define position of a predicted sample, and wT and wL are weightsassociated with reference samples in accordance with a defined position.5. A method of intra predicting a block of a picture, comprising:obtaining an intra prediction mode of a current block; and performingposition-dependent prediction combination (PDPC) based on a top sampleor a left sample when the intra prediction mode is DC mode or planarmode, wherein a top-left sample is not used for position-dependentprediction combination (PDPC).
 6. The method of claim 5, wherein whenpredModeIntra is equal to INTRA_PLANAR or INTRA_DC, the method furthercomprises applying:wT[y]=32>>((y<<1)>>nScale)wL[x]=32>>((x<<1)>>nScale)wTL[x][y]=0; and wherein predModeIntra indicates the intra predictionmode, {x,y} define position of a predicted sample, wT, wL and wTL areweights associated with reference samples in accordance with a definedposition, and nScale is a scaling parameter.
 7. An apparatus,comprising: one or more processors; and a non-transitorycomputer-readable storage medium coupled to the one or more processorsand storing executable code, which when executed by the processors,configures the apparatus to perform operations according to claim
 1. 8.A non-transitory recording medium having instructions stored thereon,which when executed by an apparatus comprising a processing, cause theapparatus to perform operations according to claim 1 for generating apredictive-encoded bit stream decoded by the apparatus and stored by thenon-transitory recording medium.
 9. A method of intra predicting a blockof a picture, comprising: obtaining a predicted sample value from one ormore reference sample values by intra-prediction using an intraprediction mode; obtaining values of nearest reference samples locatedabove and to a left of a predicted sample; obtaining at least oneadditional reference sample value in accordance with the intraprediction mode; obtaining a thresholded additional reference samplevalue based on the at least one additional reference sample value;calculating an additional value from the thresholded additionalreference sample value; multiplying the predicted sample value by asample weighting factor to generate a weighted predicted sample value;adding the additional value to the weighted predicted sample value togenerate a non-normalized predicted sample value; and normalizing thenon-normalized predicted sample value to generate a normalized predictedsample value.
 10. The method of claim 9, wherein the intra predictionmode is a vertical intra prediction mode, and wherein the at least oneadditional reference sample value is set equal to a difference between avalue of a nearest reference sample located above the predicted sampleand a value of a top-left reference sample.
 11. The method of claim 9,wherein the intra prediction mode is a horizontal intra prediction mode,and wherein the at least one additional reference sample value is setequal to a difference between a value of a nearest reference samplelocated to a left of the predicted sample and a value of a top-leftreference sample.
 12. The method of claim 9, wherein obtaining thethresholded additional reference sample value comprises: thresholdingthe additional reference sample value when the intra prediction mode ishorizontal intra prediction mode or vertical intra prediction mode toobtain the thresholded additional reference sample value.
 13. The methodof claim 9, wherein obtaining the thresholded additional referencesample value comprises: obtaining a top-left reference sample value; andupdating the at least one additional reference sample value to obtainthe thresholded additional reference sample value by checking whetherthe at least one additional reference sample value is greater than anupper limit or lower than a lower limit, wherein selection between theupper limit and the lower limit is determined based on whether atop-left reference sample value is greater than the predicted samplevalue.
 14. The method of claim 13, wherein the method further comprises:deriving minimum and maximum values of the predicted sample.
 15. Themethod of claim 14, wherein when a top-left reference sample is greaterthan or equal to the predicted sample, an upper limit is obtained bysubtracting the predicted sample value from a maximum value of thepredicted sample, the thresholded additional reference sample value isset equal to a maximum of a first value and a second value, and whereinthe first value is the additional reference sample value, and the secondvalue is the upper limit.
 16. The method of claim 14, wherein when atop-left reference sample is less than the predicted sample, a lowerlimit is obtained by subtracting the predicted sample value from aminimum value of the predicted sample, the thresholded additionalreference sample value is set equal to a minimum of a first value and asecond value, and wherein the first value is the additional referencesample value, and the second value is the lower limit.
 17. The method ofclaim 14, wherein maximum and minimum values of the predicted sample arederived from picture parameter set (PPS) values, or indicated in a sliceheader.
 18. The method of claim 9, wherein calculating the additionalvalue from the thresholded additional reference sample value comprises:calculating the additional value by multiplying a weighting factor bythe thresholded additional reference sample value when the intraprediction mode is either horizontal or vertical.
 19. The method ofclaim 9, wherein the sample weighting factor is set equal to one whenthe intra prediction mode is horizontal intra prediction mode orvertical intra prediction mode.
 20. The method of claim 9, wherein theintra prediction mode is DC intra prediction mode, and the at least oneadditional reference sample value includes a first additional referencesample value and a second additional reference sample value, and whereinthe first additional reference sample value and the second additionalreference sample value are obtained by: setting the first additionalreference sample value equal to a nearest reference sample located to aleft of the predicted sample, and setting the second additionalreference sample value equal to a nearest reference sample located abovethe predicted sample; and wherein calculating the additional valuecomprises: calculating a weighted sum of a first additional referencesample value and a second additional reference sample value when theintra prediction mode is DC intra prediction mode, wherein the weightedsum is set as the additional value.